Regenerate the test files

22 files changed, 639 insertions, 669 deletions

diff --git a/tests/fstar/arrays/Arrays.Funs.fst b/tests/fstar/arrays/Arrays.Funs.fst
index 731c7290..983b3761 100644
--- a/tests/fstar/arrays/Arrays.Funs.fst
+++ b/tests/fstar/arrays/Arrays.Funs.fst
@@ -28,17 +28,17 @@ let array_to_mut_slice_
 (** [arrays::array_len]:
     Source: 'src/arrays.rs', lines 25:0-25:40 *)
 let array_len (t : Type0) (s : array t 32) : result usize =
-  let* s1 = array_to_slice t 32 s in Return (slice_len t s1)
+  let* s1 = array_to_slice t 32 s in Ok (slice_len t s1)
 
 (** [arrays::shared_array_len]:
     Source: 'src/arrays.rs', lines 29:0-29:48 *)
 let shared_array_len (t : Type0) (s : array t 32) : result usize =
-  let* s1 = array_to_slice t 32 s in Return (slice_len t s1)
+  let* s1 = array_to_slice t 32 s in Ok (slice_len t s1)
 
 (** [arrays::shared_slice_len]:
     Source: 'src/arrays.rs', lines 33:0-33:44 *)
 let shared_slice_len (t : Type0) (s : slice t) : result usize =
-  Return (slice_len t s)
+  Ok (slice_len t s)
 
 (** [arrays::index_array_shared]:
     Source: 'src/arrays.rs', lines 37:0-37:57 *)
@@ -94,7 +94,7 @@ let slice_subslice_mut_
     core_slice_index_Slice_index_mut u32 (core_ops_range_Range usize)
       (core_slice_index_SliceIndexRangeUsizeSliceTInst u32) x
       { start = y; end_ = z } in
-  Return (s, index_mut_back)
+  Ok (s, index_mut_back)
 
 (** [arrays::array_to_slice_shared_]:
     Source: 'src/arrays.rs', lines 72:0-72:54 *)
@@ -129,7 +129,7 @@ let array_subslice_mut_
       (core_ops_index_IndexMutSliceTIInst u32 (core_ops_range_Range usize)
       (core_slice_index_SliceIndexRangeUsizeSliceTInst u32)) x
       { start = y; end_ = z } in
-  Return (s, index_mut_back)
+  Ok (s, index_mut_back)
 
 (** [arrays::index_slice_0]:
     Source: 'src/arrays.rs', lines 88:0-88:38 *)
@@ -156,42 +156,42 @@ let update_update_array
   let* (_, index_mut_back1) = array_index_mut_usize u32 32 a j in
   let* a1 = index_mut_back1 0 in
   let* _ = index_mut_back a1 in
-  Return ()
+  Ok ()
 
 (** [arrays::array_local_deep_copy]:
     Source: 'src/arrays.rs', lines 118:0-118:43 *)
 let array_local_deep_copy (x : array u32 32) : result unit =
-  Return ()
+  Ok ()
 
 (** [arrays::take_array]:
     Source: 'src/arrays.rs', lines 122:0-122:30 *)
 let take_array (a : array u32 2) : result unit =
-  Return ()
+  Ok ()
 
 (** [arrays::take_array_borrow]:
     Source: 'src/arrays.rs', lines 123:0-123:38 *)
 let take_array_borrow (a : array u32 2) : result unit =
-  Return ()
+  Ok ()
 
 (** [arrays::take_slice]:
     Source: 'src/arrays.rs', lines 124:0-124:28 *)
 let take_slice (s : slice u32) : result unit =
-  Return ()
+  Ok ()
 
 (** [arrays::take_mut_slice]:
     Source: 'src/arrays.rs', lines 125:0-125:36 *)
 let take_mut_slice (s : slice u32) : result (slice u32) =
-  Return s
+  Ok s
 
 (** [arrays::const_array]:
     Source: 'src/arrays.rs', lines 127:0-127:32 *)
 let const_array : result (array u32 2) =
-  Return (mk_array u32 2 [ 0; 0 ])
+  Ok (mk_array u32 2 [ 0; 0 ])
 
 (** [arrays::const_slice]:
     Source: 'src/arrays.rs', lines 131:0-131:20 *)
 let const_slice : result unit =
-  let* _ = array_to_slice u32 2 (mk_array u32 2 [ 0; 0 ]) in Return ()
+  let* _ = array_to_slice u32 2 (mk_array u32 2 [ 0; 0 ]) in Ok ()
 
 (** [arrays::take_all]:
     Source: 'src/arrays.rs', lines 141:0-141:17 *)
@@ -205,7 +205,7 @@ let take_all : result unit =
     array_to_slice_mut u32 2 (mk_array u32 2 [ 0; 0 ]) in
   let* s2 = take_mut_slice s1 in
   let* _ = to_slice_mut_back s2 in
-  Return ()
+  Ok ()
 
 (** [arrays::index_array]:
     Source: 'src/arrays.rs', lines 155:0-155:38 *)
@@ -225,7 +225,7 @@ let index_slice_u32_0 (x : slice u32) : result u32 =
 (** [arrays::index_mut_slice_u32_0]:
     Source: 'src/arrays.rs', lines 166:0-166:50 *)
 let index_mut_slice_u32_0 (x : slice u32) : result (u32 & (slice u32)) =
-  let* i = slice_index_usize u32 x 0 in Return (i, x)
+  let* i = slice_index_usize u32 x 0 in Ok (i, x)
 
 (** [arrays::index_all]:
     Source: 'src/arrays.rs', lines 170:0-170:25 *)
@@ -243,14 +243,14 @@ let index_all : result u32 =
   let* (i7, s2) = index_mut_slice_u32_0 s1 in
   let* i8 = u32_add i6 i7 in
   let* _ = to_slice_mut_back s2 in
-  Return i8
+  Ok i8
 
 (** [arrays::update_array]:
     Source: 'src/arrays.rs', lines 184:0-184:36 *)
 let update_array (x : array u32 2) : result unit =
   let* (_, index_mut_back) = array_index_mut_usize u32 2 x 0 in
   let* _ = index_mut_back 1 in
-  Return ()
+  Ok ()
 
 (** [arrays::update_array_mut_borrow]:
     Source: 'src/arrays.rs', lines 187:0-187:48 *)
@@ -272,7 +272,7 @@ let update_all : result unit =
   let* (s, to_slice_mut_back) = array_to_slice_mut u32 2 x in
   let* s1 = update_mut_slice s in
   let* _ = to_slice_mut_back s1 in
-  Return ()
+  Ok ()
 
 (** [arrays::range_all]:
     Source: 'src/arrays.rs', lines 205:0-205:18 *)
@@ -284,7 +284,7 @@ let range_all : result unit =
       (mk_array u32 4 [ 0; 0; 0; 0 ]) { start = 1; end_ = 3 } in
   let* s1 = update_mut_slice s in
   let* _ = index_mut_back s1 in
-  Return ()
+  Ok ()
 
 (** [arrays::deref_array_borrow]:
     Source: 'src/arrays.rs', lines 214:0-214:46 *)
@@ -294,12 +294,12 @@ let deref_array_borrow (x : array u32 2) : result u32 =
 (** [arrays::deref_array_mut_borrow]:
     Source: 'src/arrays.rs', lines 219:0-219:54 *)
 let deref_array_mut_borrow (x : array u32 2) : result (u32 & (array u32 2)) =
-  let* i = array_index_usize u32 2 x 0 in Return (i, x)
+  let* i = array_index_usize u32 2 x 0 in Ok (i, x)
 
 (** [arrays::take_array_t]:
     Source: 'src/arrays.rs', lines 227:0-227:31 *)
 let take_array_t (a : array aB_t 2) : result unit =
-  Return ()
+  Ok ()
 
 (** [arrays::non_copyable_array]:
     Source: 'src/arrays.rs', lines 229:0-229:27 *)
@@ -319,7 +319,7 @@ let rec sum_loop
     let* sum3 = u32_add sum1 i2 in
     let* i3 = usize_add i 1 in
     sum_loop s sum3 i3
-  else Return sum1
+  else Ok sum1
 
 (** [arrays::sum]:
     Source: 'src/arrays.rs', lines 242:0-242:28 *)
@@ -341,7 +341,7 @@ let rec sum2_loop
     let* sum3 = u32_add sum1 i4 in
     let* i5 = usize_add i 1 in
     sum2_loop s s2 sum3 i5
-  else Return sum1
+  else Ok sum1
 
 (** [arrays::sum2]:
     Source: 'src/arrays.rs', lines 252:0-252:41 *)
@@ -358,7 +358,7 @@ let f0 : result unit =
   let* (_, index_mut_back) = slice_index_mut_usize u32 s 0 in
   let* s1 = index_mut_back 1 in
   let* _ = to_slice_mut_back s1 in
-  Return ()
+  Ok ()
 
 (** [arrays::f1]:
     Source: 'src/arrays.rs', lines 268:0-268:11 *)
@@ -366,12 +366,12 @@ let f1 : result unit =
   let* (_, index_mut_back) =
     array_index_mut_usize u32 2 (mk_array u32 2 [ 1; 2 ]) 0 in
   let* _ = index_mut_back 1 in
-  Return ()
+  Ok ()
 
 (** [arrays::f2]:
     Source: 'src/arrays.rs', lines 273:0-273:17 *)
 let f2 (i : u32) : result unit =
-  Return ()
+  Ok ()
 
 (** [arrays::f4]:
     Source: 'src/arrays.rs', lines 282:0-282:54 *)
@@ -393,7 +393,7 @@ let f3 : result u32 =
 
 (** [arrays::SZ]
     Source: 'src/arrays.rs', lines 286:0-286:19 *)
-let sz_body : result usize = Return 32
+let sz_body : result usize = Ok 32
 let sz : usize = eval_global sz_body
 
 (** [arrays::f5]:
@@ -412,7 +412,7 @@ let ite : result unit =
   let* (_, s3) = index_mut_slice_u32_0 s2 in
   let* _ = to_slice_mut_back1 s3 in
   let* _ = to_slice_mut_back s1 in
-  Return ()
+  Ok ()
 
 (** [arrays::zero_slice]: loop 0:
     Source: 'src/arrays.rs', lines 303:0-310:1 *)
@@ -426,7 +426,7 @@ let rec zero_slice_loop
     let* i1 = usize_add i 1 in
     let* a1 = index_mut_back 0 in
     zero_slice_loop a1 i1 len
-  else Return a
+  else Ok a
 
 (** [arrays::zero_slice]:
     Source: 'src/arrays.rs', lines 303:0-303:31 *)
@@ -441,12 +441,12 @@ let rec iter_mut_slice_loop
   =
   if i < len
   then let* i1 = usize_add i 1 in iter_mut_slice_loop len i1
-  else Return ()
+  else Ok ()
 
 (** [arrays::iter_mut_slice]:
     Source: 'src/arrays.rs', lines 312:0-312:35 *)
 let iter_mut_slice (a : slice u8) : result (slice u8) =
-  let len = slice_len u8 a in let* _ = iter_mut_slice_loop len 0 in Return a
+  let len = slice_len u8 a in let* _ = iter_mut_slice_loop len 0 in Ok a
 
 (** [arrays::sum_mut_slice]: loop 0:
     Source: 'src/arrays.rs', lines 320:0-328:1 *)
@@ -461,10 +461,10 @@ let rec sum_mut_slice_loop
     let* s1 = u32_add s i2 in
     let* i3 = usize_add i 1 in
     sum_mut_slice_loop a i3 s1
-  else Return s
+  else Ok s
 
 (** [arrays::sum_mut_slice]:
     Source: 'src/arrays.rs', lines 320:0-320:42 *)
 let sum_mut_slice (a : slice u32) : result (u32 & (slice u32)) =
-  let* i = sum_mut_slice_loop a 0 0 in Return (i, a)
+  let* i = sum_mut_slice_loop a 0 0 in Ok (i, a)
 
diff --git a/tests/fstar/arrays/Primitives.fst b/tests/fstar/arrays/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/arrays/Primitives.fst
+++ b/tests/fstar/arrays/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/betree/BetreeMain.Funs.fst b/tests/fstar/betree/BetreeMain.Funs.fst
index 129e6f7e..8e64f43f 100644
--- a/tests/fstar/betree/BetreeMain.Funs.fst
+++ b/tests/fstar/betree/BetreeMain.Funs.fst
@@ -41,19 +41,19 @@ let betree_store_leaf_node
 (** [betree_main::betree::fresh_node_id]:
     Source: 'src/betree.rs', lines 55:0-55:48 *)
 let betree_fresh_node_id (counter : u64) : result (u64 & u64) =
-  let* counter1 = u64_add counter 1 in Return (counter, counter1)
+  let* counter1 = u64_add counter 1 in Ok (counter, counter1)
 
 (** [betree_main::betree::{betree_main::betree::NodeIdCounter}::new]:
     Source: 'src/betree.rs', lines 206:4-206:20 *)
 let betree_NodeIdCounter_new : result betree_NodeIdCounter_t =
-  Return { next_node_id = 0 }
+  Ok { next_node_id = 0 }
 
 (** [betree_main::betree::{betree_main::betree::NodeIdCounter}::fresh_id]:
     Source: 'src/betree.rs', lines 210:4-210:36 *)
 let betree_NodeIdCounter_fresh_id
   (self : betree_NodeIdCounter_t) : result (u64 & betree_NodeIdCounter_t) =
   let* i = u64_add self.next_node_id 1 in
-  Return (self.next_node_id, { next_node_id = i })
+  Ok (self.next_node_id, { next_node_id = i })
 
 (** [betree_main::betree::upsert_update]:
     Source: 'src/betree.rs', lines 234:0-234:70 *)
@@ -62,16 +62,16 @@ let betree_upsert_update
   begin match prev with
   | None ->
     begin match st with
-    | Betree_UpsertFunState_Add v -> Return v
-    | Betree_UpsertFunState_Sub _ -> Return 0
+    | Betree_UpsertFunState_Add v -> Ok v
+    | Betree_UpsertFunState_Sub _ -> Ok 0
     end
   | Some prev1 ->
     begin match st with
     | Betree_UpsertFunState_Add v ->
       let* margin = u64_sub core_u64_max prev1 in
-      if margin >= v then u64_add prev1 v else Return core_u64_max
+      if margin >= v then u64_add prev1 v else Ok core_u64_max
     | Betree_UpsertFunState_Sub v ->
-      if prev1 >= v then u64_sub prev1 v else Return 0
+      if prev1 >= v then u64_sub prev1 v else Ok 0
     end
   end
 
@@ -83,7 +83,7 @@ let rec betree_List_len
   =
   begin match self with
   | Betree_List_Cons _ tl -> let* i = betree_List_len t tl in u64_add 1 i
-  | Betree_List_Nil -> Return 0
+  | Betree_List_Nil -> Ok 0
   end
 
 (** [betree_main::betree::{betree_main::betree::List<T>#1}::split_at]:
@@ -94,14 +94,14 @@ let rec betree_List_split_at
   (decreases (betree_List_split_at_decreases t self n))
   =
   if n = 0
-  then Return (Betree_List_Nil, self)
+  then Ok (Betree_List_Nil, self)
   else
     begin match self with
     | Betree_List_Cons hd tl ->
       let* i = u64_sub n 1 in
       let* p = betree_List_split_at t tl i in
       let (ls0, ls1) = p in
-      Return (Betree_List_Cons hd ls0, ls1)
+      Ok (Betree_List_Cons hd ls0, ls1)
     | Betree_List_Nil -> Fail Failure
     end
 
@@ -110,7 +110,7 @@ let rec betree_List_split_at
 let betree_List_push_front
   (t : Type0) (self : betree_List_t t) (x : t) : result (betree_List_t t) =
   let (tl, _) = core_mem_replace (betree_List_t t) self Betree_List_Nil in
-  Return (Betree_List_Cons x tl)
+  Ok (Betree_List_Cons x tl)
 
 (** [betree_main::betree::{betree_main::betree::List<T>#1}::pop_front]:
     Source: 'src/betree.rs', lines 306:4-306:32 *)
@@ -118,7 +118,7 @@ let betree_List_pop_front
   (t : Type0) (self : betree_List_t t) : result (t & (betree_List_t t)) =
   let (ls, _) = core_mem_replace (betree_List_t t) self Betree_List_Nil in
   begin match ls with
-  | Betree_List_Cons x tl -> Return (x, tl)
+  | Betree_List_Cons x tl -> Ok (x, tl)
   | Betree_List_Nil -> Fail Failure
   end
 
@@ -126,7 +126,7 @@ let betree_List_pop_front
     Source: 'src/betree.rs', lines 318:4-318:22 *)
 let betree_List_hd (t : Type0) (self : betree_List_t t) : result t =
   begin match self with
-  | Betree_List_Cons hd _ -> Return hd
+  | Betree_List_Cons hd _ -> Ok hd
   | Betree_List_Nil -> Fail Failure
   end
 
@@ -135,8 +135,8 @@ let betree_List_hd (t : Type0) (self : betree_List_t t) : result t =
 let betree_ListPairU64T_head_has_key
   (t : Type0) (self : betree_List_t (u64 & t)) (key : u64) : result bool =
   begin match self with
-  | Betree_List_Cons hd _ -> let (i, _) = hd in Return (i = key)
-  | Betree_List_Nil -> Return false
+  | Betree_List_Cons hd _ -> let (i, _) = hd in Ok (i = key)
+  | Betree_List_Nil -> Ok false
   end
 
 (** [betree_main::betree::{betree_main::betree::List<(u64, T)>#2}::partition_at_pivot]:
@@ -150,12 +150,12 @@ let rec betree_ListPairU64T_partition_at_pivot
   | Betree_List_Cons hd tl ->
     let (i, x) = hd in
     if i >= pivot
-    then Return (Betree_List_Nil, Betree_List_Cons (i, x) tl)
+    then Ok (Betree_List_Nil, Betree_List_Cons (i, x) tl)
     else
       let* p = betree_ListPairU64T_partition_at_pivot t tl pivot in
       let (ls0, ls1) = p in
-      Return (Betree_List_Cons (i, x) ls0, ls1)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Betree_List_Nil)
+      Ok (Betree_List_Cons (i, x) ls0, ls1)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Betree_List_Nil)
   end
 
 (** [betree_main::betree::{betree_main::betree::Leaf#3}::split]:
@@ -176,7 +176,7 @@ let betree_Leaf_split
   let* (st2, _) = betree_store_leaf_node id1 content1 st1 in
   let n = Betree_Node_Leaf { id = id0; size = params.split_size } in
   let n1 = Betree_Node_Leaf { id = id1; size = params.split_size } in
-  Return (st2, ({ id = self.id; pivot = pivot; left = n; right = n1 },
+  Ok (st2, ({ id = self.id; pivot = pivot; left = n; right = n1 },
     node_id_cnt2))
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_first_message_for_key]:
@@ -191,16 +191,16 @@ let rec betree_Node_lookup_first_message_for_key
   | Betree_List_Cons x next_msgs ->
     let (i, m) = x in
     if i >= key
-    then Return (Betree_List_Cons (i, m) next_msgs, Return)
+    then Ok (Betree_List_Cons (i, m) next_msgs, Ok)
     else
       let* (l, lookup_first_message_for_key_back) =
         betree_Node_lookup_first_message_for_key key next_msgs in
       let back =
         fun ret ->
           let* next_msgs1 = lookup_first_message_for_key_back ret in
-          Return (Betree_List_Cons (i, m) next_msgs1) in
-      Return (l, back)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Return)
+          Ok (Betree_List_Cons (i, m) next_msgs1) in
+      Ok (l, back)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Ok)
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_in_bindings]:
@@ -214,9 +214,9 @@ let rec betree_Node_lookup_in_bindings
   | Betree_List_Cons hd tl ->
     let (i, i1) = hd in
     if i = key
-    then Return (Some i1)
-    else if i > key then Return None else betree_Node_lookup_in_bindings key tl
-  | Betree_List_Nil -> Return None
+    then Ok (Some i1)
+    else if i > key then Ok None else betree_Node_lookup_in_bindings key tl
+  | Betree_List_Nil -> Ok None
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_upserts]:
@@ -244,7 +244,7 @@ let rec betree_Node_apply_upserts
     let* msgs1 =
       betree_List_push_front (u64 & betree_Message_t) msgs (key,
         Betree_Message_Insert v) in
-    Return (st1, (v, msgs1))
+    Ok (st1, (v, msgs1))
 
 (** [betree_main::betree::{betree_main::betree::Internal#4}::lookup_in_children]:
     Source: 'src/betree.rs', lines 395:4-395:63 *)
@@ -256,10 +256,10 @@ let rec betree_Internal_lookup_in_children
   if key < self.pivot
   then
     let* (st1, (o, n)) = betree_Node_lookup self.left key st in
-    Return (st1, (o, { self with left = n }))
+    Ok (st1, (o, { self with left = n }))
   else
     let* (st1, (o, n)) = betree_Node_lookup self.right key st in
-    Return (st1, (o, { self with right = n }))
+    Ok (st1, (o, { self with right = n }))
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup]:
     Source: 'src/betree.rs', lines 709:4-709:58 *)
@@ -282,19 +282,19 @@ and betree_Node_lookup
           betree_Internal_lookup_in_children node key st1 in
         let* _ =
           lookup_first_message_for_key_back (Betree_List_Cons (k, msg) l) in
-        Return (st2, (o, Betree_Node_Internal node1))
+        Ok (st2, (o, Betree_Node_Internal node1))
       else
         begin match msg with
         | Betree_Message_Insert v ->
           let* _ =
             lookup_first_message_for_key_back (Betree_List_Cons (k,
               Betree_Message_Insert v) l) in
-          Return (st1, (Some v, Betree_Node_Internal node))
+          Ok (st1, (Some v, Betree_Node_Internal node))
         | Betree_Message_Delete ->
           let* _ =
             lookup_first_message_for_key_back (Betree_List_Cons (k,
               Betree_Message_Delete) l) in
-          Return (st1, (None, Betree_Node_Internal node))
+          Ok (st1, (None, Betree_Node_Internal node))
         | Betree_Message_Upsert ufs ->
           let* (st2, (v, node1)) =
             betree_Internal_lookup_in_children node key st1 in
@@ -303,18 +303,18 @@ and betree_Node_lookup
               Betree_Message_Upsert ufs) l) v key st2 in
           let* msgs1 = lookup_first_message_for_key_back pending1 in
           let* (st4, _) = betree_store_internal_node node1.id msgs1 st3 in
-          Return (st4, (Some v1, Betree_Node_Internal node1))
+          Ok (st4, (Some v1, Betree_Node_Internal node1))
         end
     | Betree_List_Nil ->
       let* (st2, (o, node1)) = betree_Internal_lookup_in_children node key st1
         in
       let* _ = lookup_first_message_for_key_back Betree_List_Nil in
-      Return (st2, (o, Betree_Node_Internal node1))
+      Ok (st2, (o, Betree_Node_Internal node1))
     end
   | Betree_Node_Leaf node ->
     let* (st1, bindings) = betree_load_leaf_node node.id st in
     let* o = betree_Node_lookup_in_bindings key bindings in
-    Return (st1, (o, Betree_Node_Leaf node))
+    Ok (st1, (o, Betree_Node_Leaf node))
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::filter_messages_for_key]:
@@ -333,8 +333,8 @@ let rec betree_Node_filter_messages_for_key
         betree_List_pop_front (u64 & betree_Message_t) (Betree_List_Cons (k, m)
           l) in
       betree_Node_filter_messages_for_key key msgs1
-    else Return (Betree_List_Cons (k, m) l)
-  | Betree_List_Nil -> Return Betree_List_Nil
+    else Ok (Betree_List_Cons (k, m) l)
+  | Betree_List_Nil -> Ok Betree_List_Nil
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_first_message_after_key]:
@@ -355,10 +355,10 @@ let rec betree_Node_lookup_first_message_after_key
       let back =
         fun ret ->
           let* next_msgs1 = lookup_first_message_after_key_back ret in
-          Return (Betree_List_Cons (k, m) next_msgs1) in
-      Return (l, back)
-    else Return (Betree_List_Cons (k, m) next_msgs, Return)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Return)
+          Ok (Betree_List_Cons (k, m) next_msgs1) in
+      Ok (l, back)
+    else Ok (Betree_List_Cons (k, m) next_msgs, Ok)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Ok)
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_to_internal]:
@@ -434,7 +434,7 @@ let rec betree_Node_apply_messages_to_internal
     let (i, m) = new_msg in
     let* msgs1 = betree_Node_apply_to_internal msgs i m in
     betree_Node_apply_messages_to_internal msgs1 new_msgs_tl
-  | Betree_List_Nil -> Return msgs
+  | Betree_List_Nil -> Ok msgs
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_mut_in_bindings]:
@@ -449,16 +449,16 @@ let rec betree_Node_lookup_mut_in_bindings
   | Betree_List_Cons hd tl ->
     let (i, i1) = hd in
     if i >= key
-    then Return (Betree_List_Cons (i, i1) tl, Return)
+    then Ok (Betree_List_Cons (i, i1) tl, Ok)
     else
       let* (l, lookup_mut_in_bindings_back) =
         betree_Node_lookup_mut_in_bindings key tl in
       let back =
         fun ret ->
           let* tl1 = lookup_mut_in_bindings_back ret in
-          Return (Betree_List_Cons (i, i1) tl1) in
-      Return (l, back)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Return)
+          Ok (Betree_List_Cons (i, i1) tl1) in
+      Ok (l, back)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Ok)
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_to_leaf]:
@@ -510,7 +510,7 @@ let rec betree_Node_apply_messages_to_leaf
     let (i, m) = new_msg in
     let* bindings1 = betree_Node_apply_to_leaf bindings i m in
     betree_Node_apply_messages_to_leaf bindings1 new_msgs_tl
-  | Betree_List_Nil -> Return bindings
+  | Betree_List_Nil -> Ok bindings
   end
 
 (** [betree_main::betree::{betree_main::betree::Internal#4}::flush]:
@@ -541,14 +541,14 @@ let rec betree_Internal_flush
         betree_Node_apply_messages self.right params node_id_cnt1 msgs_right
           st1 in
       let (n1, node_id_cnt2) = p2 in
-      Return (st2, (Betree_List_Nil, ({ self with left = n; right = n1 },
+      Ok (st2, (Betree_List_Nil, ({ self with left = n; right = n1 },
         node_id_cnt2)))
-    else Return (st1, (msgs_right, ({ self with left = n }, node_id_cnt1)))
+    else Ok (st1, (msgs_right, ({ self with left = n }, node_id_cnt1)))
   else
     let* (st1, p1) =
       betree_Node_apply_messages self.right params node_id_cnt msgs_right st in
     let (n, node_id_cnt1) = p1 in
-    Return (st1, (msgs_left, ({ self with right = n }, node_id_cnt1)))
+    Ok (st1, (msgs_left, ({ self with right = n }, node_id_cnt1)))
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_messages]:
     Source: 'src/betree.rs', lines 588:4-593:5 *)
@@ -571,10 +571,10 @@ and betree_Node_apply_messages
         betree_Internal_flush node params node_id_cnt content1 st1 in
       let (node1, node_id_cnt1) = p in
       let* (st3, _) = betree_store_internal_node node1.id content2 st2 in
-      Return (st3, (Betree_Node_Internal node1, node_id_cnt1))
+      Ok (st3, (Betree_Node_Internal node1, node_id_cnt1))
     else
       let* (st2, _) = betree_store_internal_node node.id content1 st1 in
-      Return (st2, (Betree_Node_Internal node, node_id_cnt))
+      Ok (st2, (Betree_Node_Internal node, node_id_cnt))
   | Betree_Node_Leaf node ->
     let* (st1, content) = betree_load_leaf_node node.id st in
     let* content1 = betree_Node_apply_messages_to_leaf content msgs in
@@ -585,10 +585,10 @@ and betree_Node_apply_messages
       let* (st2, (new_node, node_id_cnt1)) =
         betree_Leaf_split node content1 params node_id_cnt st1 in
       let* (st3, _) = betree_store_leaf_node node.id Betree_List_Nil st2 in
-      Return (st3, (Betree_Node_Internal new_node, node_id_cnt1))
+      Ok (st3, (Betree_Node_Internal new_node, node_id_cnt1))
     else
       let* (st2, _) = betree_store_leaf_node node.id content1 st1 in
-      Return (st2, (Betree_Node_Leaf { node with size = len }, node_id_cnt))
+      Ok (st2, (Betree_Node_Leaf { node with size = len }, node_id_cnt))
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply]:
@@ -603,7 +603,7 @@ let betree_Node_apply
     betree_Node_apply_messages self params node_id_cnt (Betree_List_Cons (key,
       new_msg) Betree_List_Nil) st in
   let (self1, node_id_cnt1) = p in
-  Return (st1, (self1, node_id_cnt1))
+  Ok (st1, (self1, node_id_cnt1))
 
 (** [betree_main::betree::{betree_main::betree::BeTree#6}::new]:
     Source: 'src/betree.rs', lines 849:4-849:60 *)
@@ -614,7 +614,7 @@ let betree_BeTree_new
   let* node_id_cnt = betree_NodeIdCounter_new in
   let* (id, node_id_cnt1) = betree_NodeIdCounter_fresh_id node_id_cnt in
   let* (st1, _) = betree_store_leaf_node id Betree_List_Nil st in
-  Return (st1,
+  Ok (st1,
     {
       params = { min_flush_size = min_flush_size; split_size = split_size };
       node_id_cnt = node_id_cnt1;
@@ -630,7 +630,7 @@ let betree_BeTree_apply
   let* (st1, p) =
     betree_Node_apply self.root self.params self.node_id_cnt key msg st in
   let (n, nic) = p in
-  Return (st1, { self with node_id_cnt = nic; root = n })
+  Ok (st1, { self with node_id_cnt = nic; root = n })
 
 (** [betree_main::betree::{betree_main::betree::BeTree#6}::insert]:
     Source: 'src/betree.rs', lines 874:4-874:52 *)
@@ -664,13 +664,13 @@ let betree_BeTree_lookup
   result (state & ((option u64) & betree_BeTree_t))
   =
   let* (st1, (o, n)) = betree_Node_lookup self.root key st in
-  Return (st1, (o, { self with root = n }))
+  Ok (st1, (o, { self with root = n }))
 
 (** [betree_main::main]:
     Source: 'src/betree_main.rs', lines 5:0-5:9 *)
 let main : result unit =
-  Return ()
+  Ok ()
 
 (** Unit test for [betree_main::main] *)
-let _ = assert_norm (main = Return ())
+let _ = assert_norm (main = Ok ())
 
diff --git a/tests/fstar/betree/Primitives.fst b/tests/fstar/betree/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/betree/Primitives.fst
+++ b/tests/fstar/betree/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/betree_back_stateful/BetreeMain.Funs.fst b/tests/fstar/betree_back_stateful/BetreeMain.Funs.fst
index 129e6f7e..8e64f43f 100644
--- a/tests/fstar/betree_back_stateful/BetreeMain.Funs.fst
+++ b/tests/fstar/betree_back_stateful/BetreeMain.Funs.fst
@@ -41,19 +41,19 @@ let betree_store_leaf_node
 (** [betree_main::betree::fresh_node_id]:
     Source: 'src/betree.rs', lines 55:0-55:48 *)
 let betree_fresh_node_id (counter : u64) : result (u64 & u64) =
-  let* counter1 = u64_add counter 1 in Return (counter, counter1)
+  let* counter1 = u64_add counter 1 in Ok (counter, counter1)
 
 (** [betree_main::betree::{betree_main::betree::NodeIdCounter}::new]:
     Source: 'src/betree.rs', lines 206:4-206:20 *)
 let betree_NodeIdCounter_new : result betree_NodeIdCounter_t =
-  Return { next_node_id = 0 }
+  Ok { next_node_id = 0 }
 
 (** [betree_main::betree::{betree_main::betree::NodeIdCounter}::fresh_id]:
     Source: 'src/betree.rs', lines 210:4-210:36 *)
 let betree_NodeIdCounter_fresh_id
   (self : betree_NodeIdCounter_t) : result (u64 & betree_NodeIdCounter_t) =
   let* i = u64_add self.next_node_id 1 in
-  Return (self.next_node_id, { next_node_id = i })
+  Ok (self.next_node_id, { next_node_id = i })
 
 (** [betree_main::betree::upsert_update]:
     Source: 'src/betree.rs', lines 234:0-234:70 *)
@@ -62,16 +62,16 @@ let betree_upsert_update
   begin match prev with
   | None ->
     begin match st with
-    | Betree_UpsertFunState_Add v -> Return v
-    | Betree_UpsertFunState_Sub _ -> Return 0
+    | Betree_UpsertFunState_Add v -> Ok v
+    | Betree_UpsertFunState_Sub _ -> Ok 0
     end
   | Some prev1 ->
     begin match st with
     | Betree_UpsertFunState_Add v ->
       let* margin = u64_sub core_u64_max prev1 in
-      if margin >= v then u64_add prev1 v else Return core_u64_max
+      if margin >= v then u64_add prev1 v else Ok core_u64_max
     | Betree_UpsertFunState_Sub v ->
-      if prev1 >= v then u64_sub prev1 v else Return 0
+      if prev1 >= v then u64_sub prev1 v else Ok 0
     end
   end
 
@@ -83,7 +83,7 @@ let rec betree_List_len
   =
   begin match self with
   | Betree_List_Cons _ tl -> let* i = betree_List_len t tl in u64_add 1 i
-  | Betree_List_Nil -> Return 0
+  | Betree_List_Nil -> Ok 0
   end
 
 (** [betree_main::betree::{betree_main::betree::List<T>#1}::split_at]:
@@ -94,14 +94,14 @@ let rec betree_List_split_at
   (decreases (betree_List_split_at_decreases t self n))
   =
   if n = 0
-  then Return (Betree_List_Nil, self)
+  then Ok (Betree_List_Nil, self)
   else
     begin match self with
     | Betree_List_Cons hd tl ->
       let* i = u64_sub n 1 in
       let* p = betree_List_split_at t tl i in
       let (ls0, ls1) = p in
-      Return (Betree_List_Cons hd ls0, ls1)
+      Ok (Betree_List_Cons hd ls0, ls1)
     | Betree_List_Nil -> Fail Failure
     end
 
@@ -110,7 +110,7 @@ let rec betree_List_split_at
 let betree_List_push_front
   (t : Type0) (self : betree_List_t t) (x : t) : result (betree_List_t t) =
   let (tl, _) = core_mem_replace (betree_List_t t) self Betree_List_Nil in
-  Return (Betree_List_Cons x tl)
+  Ok (Betree_List_Cons x tl)
 
 (** [betree_main::betree::{betree_main::betree::List<T>#1}::pop_front]:
     Source: 'src/betree.rs', lines 306:4-306:32 *)
@@ -118,7 +118,7 @@ let betree_List_pop_front
   (t : Type0) (self : betree_List_t t) : result (t & (betree_List_t t)) =
   let (ls, _) = core_mem_replace (betree_List_t t) self Betree_List_Nil in
   begin match ls with
-  | Betree_List_Cons x tl -> Return (x, tl)
+  | Betree_List_Cons x tl -> Ok (x, tl)
   | Betree_List_Nil -> Fail Failure
   end
 
@@ -126,7 +126,7 @@ let betree_List_pop_front
     Source: 'src/betree.rs', lines 318:4-318:22 *)
 let betree_List_hd (t : Type0) (self : betree_List_t t) : result t =
   begin match self with
-  | Betree_List_Cons hd _ -> Return hd
+  | Betree_List_Cons hd _ -> Ok hd
   | Betree_List_Nil -> Fail Failure
   end
 
@@ -135,8 +135,8 @@ let betree_List_hd (t : Type0) (self : betree_List_t t) : result t =
 let betree_ListPairU64T_head_has_key
   (t : Type0) (self : betree_List_t (u64 & t)) (key : u64) : result bool =
   begin match self with
-  | Betree_List_Cons hd _ -> let (i, _) = hd in Return (i = key)
-  | Betree_List_Nil -> Return false
+  | Betree_List_Cons hd _ -> let (i, _) = hd in Ok (i = key)
+  | Betree_List_Nil -> Ok false
   end
 
 (** [betree_main::betree::{betree_main::betree::List<(u64, T)>#2}::partition_at_pivot]:
@@ -150,12 +150,12 @@ let rec betree_ListPairU64T_partition_at_pivot
   | Betree_List_Cons hd tl ->
     let (i, x) = hd in
     if i >= pivot
-    then Return (Betree_List_Nil, Betree_List_Cons (i, x) tl)
+    then Ok (Betree_List_Nil, Betree_List_Cons (i, x) tl)
     else
       let* p = betree_ListPairU64T_partition_at_pivot t tl pivot in
       let (ls0, ls1) = p in
-      Return (Betree_List_Cons (i, x) ls0, ls1)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Betree_List_Nil)
+      Ok (Betree_List_Cons (i, x) ls0, ls1)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Betree_List_Nil)
   end
 
 (** [betree_main::betree::{betree_main::betree::Leaf#3}::split]:
@@ -176,7 +176,7 @@ let betree_Leaf_split
   let* (st2, _) = betree_store_leaf_node id1 content1 st1 in
   let n = Betree_Node_Leaf { id = id0; size = params.split_size } in
   let n1 = Betree_Node_Leaf { id = id1; size = params.split_size } in
-  Return (st2, ({ id = self.id; pivot = pivot; left = n; right = n1 },
+  Ok (st2, ({ id = self.id; pivot = pivot; left = n; right = n1 },
     node_id_cnt2))
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_first_message_for_key]:
@@ -191,16 +191,16 @@ let rec betree_Node_lookup_first_message_for_key
   | Betree_List_Cons x next_msgs ->
     let (i, m) = x in
     if i >= key
-    then Return (Betree_List_Cons (i, m) next_msgs, Return)
+    then Ok (Betree_List_Cons (i, m) next_msgs, Ok)
     else
       let* (l, lookup_first_message_for_key_back) =
         betree_Node_lookup_first_message_for_key key next_msgs in
       let back =
         fun ret ->
           let* next_msgs1 = lookup_first_message_for_key_back ret in
-          Return (Betree_List_Cons (i, m) next_msgs1) in
-      Return (l, back)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Return)
+          Ok (Betree_List_Cons (i, m) next_msgs1) in
+      Ok (l, back)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Ok)
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_in_bindings]:
@@ -214,9 +214,9 @@ let rec betree_Node_lookup_in_bindings
   | Betree_List_Cons hd tl ->
     let (i, i1) = hd in
     if i = key
-    then Return (Some i1)
-    else if i > key then Return None else betree_Node_lookup_in_bindings key tl
-  | Betree_List_Nil -> Return None
+    then Ok (Some i1)
+    else if i > key then Ok None else betree_Node_lookup_in_bindings key tl
+  | Betree_List_Nil -> Ok None
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_upserts]:
@@ -244,7 +244,7 @@ let rec betree_Node_apply_upserts
     let* msgs1 =
       betree_List_push_front (u64 & betree_Message_t) msgs (key,
         Betree_Message_Insert v) in
-    Return (st1, (v, msgs1))
+    Ok (st1, (v, msgs1))
 
 (** [betree_main::betree::{betree_main::betree::Internal#4}::lookup_in_children]:
     Source: 'src/betree.rs', lines 395:4-395:63 *)
@@ -256,10 +256,10 @@ let rec betree_Internal_lookup_in_children
   if key < self.pivot
   then
     let* (st1, (o, n)) = betree_Node_lookup self.left key st in
-    Return (st1, (o, { self with left = n }))
+    Ok (st1, (o, { self with left = n }))
   else
     let* (st1, (o, n)) = betree_Node_lookup self.right key st in
-    Return (st1, (o, { self with right = n }))
+    Ok (st1, (o, { self with right = n }))
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup]:
     Source: 'src/betree.rs', lines 709:4-709:58 *)
@@ -282,19 +282,19 @@ and betree_Node_lookup
           betree_Internal_lookup_in_children node key st1 in
         let* _ =
           lookup_first_message_for_key_back (Betree_List_Cons (k, msg) l) in
-        Return (st2, (o, Betree_Node_Internal node1))
+        Ok (st2, (o, Betree_Node_Internal node1))
       else
         begin match msg with
         | Betree_Message_Insert v ->
           let* _ =
             lookup_first_message_for_key_back (Betree_List_Cons (k,
               Betree_Message_Insert v) l) in
-          Return (st1, (Some v, Betree_Node_Internal node))
+          Ok (st1, (Some v, Betree_Node_Internal node))
         | Betree_Message_Delete ->
           let* _ =
             lookup_first_message_for_key_back (Betree_List_Cons (k,
               Betree_Message_Delete) l) in
-          Return (st1, (None, Betree_Node_Internal node))
+          Ok (st1, (None, Betree_Node_Internal node))
         | Betree_Message_Upsert ufs ->
           let* (st2, (v, node1)) =
             betree_Internal_lookup_in_children node key st1 in
@@ -303,18 +303,18 @@ and betree_Node_lookup
               Betree_Message_Upsert ufs) l) v key st2 in
           let* msgs1 = lookup_first_message_for_key_back pending1 in
           let* (st4, _) = betree_store_internal_node node1.id msgs1 st3 in
-          Return (st4, (Some v1, Betree_Node_Internal node1))
+          Ok (st4, (Some v1, Betree_Node_Internal node1))
         end
     | Betree_List_Nil ->
       let* (st2, (o, node1)) = betree_Internal_lookup_in_children node key st1
         in
       let* _ = lookup_first_message_for_key_back Betree_List_Nil in
-      Return (st2, (o, Betree_Node_Internal node1))
+      Ok (st2, (o, Betree_Node_Internal node1))
     end
   | Betree_Node_Leaf node ->
     let* (st1, bindings) = betree_load_leaf_node node.id st in
     let* o = betree_Node_lookup_in_bindings key bindings in
-    Return (st1, (o, Betree_Node_Leaf node))
+    Ok (st1, (o, Betree_Node_Leaf node))
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::filter_messages_for_key]:
@@ -333,8 +333,8 @@ let rec betree_Node_filter_messages_for_key
         betree_List_pop_front (u64 & betree_Message_t) (Betree_List_Cons (k, m)
           l) in
       betree_Node_filter_messages_for_key key msgs1
-    else Return (Betree_List_Cons (k, m) l)
-  | Betree_List_Nil -> Return Betree_List_Nil
+    else Ok (Betree_List_Cons (k, m) l)
+  | Betree_List_Nil -> Ok Betree_List_Nil
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_first_message_after_key]:
@@ -355,10 +355,10 @@ let rec betree_Node_lookup_first_message_after_key
       let back =
         fun ret ->
           let* next_msgs1 = lookup_first_message_after_key_back ret in
-          Return (Betree_List_Cons (k, m) next_msgs1) in
-      Return (l, back)
-    else Return (Betree_List_Cons (k, m) next_msgs, Return)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Return)
+          Ok (Betree_List_Cons (k, m) next_msgs1) in
+      Ok (l, back)
+    else Ok (Betree_List_Cons (k, m) next_msgs, Ok)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Ok)
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_to_internal]:
@@ -434,7 +434,7 @@ let rec betree_Node_apply_messages_to_internal
     let (i, m) = new_msg in
     let* msgs1 = betree_Node_apply_to_internal msgs i m in
     betree_Node_apply_messages_to_internal msgs1 new_msgs_tl
-  | Betree_List_Nil -> Return msgs
+  | Betree_List_Nil -> Ok msgs
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::lookup_mut_in_bindings]:
@@ -449,16 +449,16 @@ let rec betree_Node_lookup_mut_in_bindings
   | Betree_List_Cons hd tl ->
     let (i, i1) = hd in
     if i >= key
-    then Return (Betree_List_Cons (i, i1) tl, Return)
+    then Ok (Betree_List_Cons (i, i1) tl, Ok)
     else
       let* (l, lookup_mut_in_bindings_back) =
         betree_Node_lookup_mut_in_bindings key tl in
       let back =
         fun ret ->
           let* tl1 = lookup_mut_in_bindings_back ret in
-          Return (Betree_List_Cons (i, i1) tl1) in
-      Return (l, back)
-  | Betree_List_Nil -> Return (Betree_List_Nil, Return)
+          Ok (Betree_List_Cons (i, i1) tl1) in
+      Ok (l, back)
+  | Betree_List_Nil -> Ok (Betree_List_Nil, Ok)
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_to_leaf]:
@@ -510,7 +510,7 @@ let rec betree_Node_apply_messages_to_leaf
     let (i, m) = new_msg in
     let* bindings1 = betree_Node_apply_to_leaf bindings i m in
     betree_Node_apply_messages_to_leaf bindings1 new_msgs_tl
-  | Betree_List_Nil -> Return bindings
+  | Betree_List_Nil -> Ok bindings
   end
 
 (** [betree_main::betree::{betree_main::betree::Internal#4}::flush]:
@@ -541,14 +541,14 @@ let rec betree_Internal_flush
         betree_Node_apply_messages self.right params node_id_cnt1 msgs_right
           st1 in
       let (n1, node_id_cnt2) = p2 in
-      Return (st2, (Betree_List_Nil, ({ self with left = n; right = n1 },
+      Ok (st2, (Betree_List_Nil, ({ self with left = n; right = n1 },
         node_id_cnt2)))
-    else Return (st1, (msgs_right, ({ self with left = n }, node_id_cnt1)))
+    else Ok (st1, (msgs_right, ({ self with left = n }, node_id_cnt1)))
   else
     let* (st1, p1) =
       betree_Node_apply_messages self.right params node_id_cnt msgs_right st in
     let (n, node_id_cnt1) = p1 in
-    Return (st1, (msgs_left, ({ self with right = n }, node_id_cnt1)))
+    Ok (st1, (msgs_left, ({ self with right = n }, node_id_cnt1)))
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply_messages]:
     Source: 'src/betree.rs', lines 588:4-593:5 *)
@@ -571,10 +571,10 @@ and betree_Node_apply_messages
         betree_Internal_flush node params node_id_cnt content1 st1 in
       let (node1, node_id_cnt1) = p in
       let* (st3, _) = betree_store_internal_node node1.id content2 st2 in
-      Return (st3, (Betree_Node_Internal node1, node_id_cnt1))
+      Ok (st3, (Betree_Node_Internal node1, node_id_cnt1))
     else
       let* (st2, _) = betree_store_internal_node node.id content1 st1 in
-      Return (st2, (Betree_Node_Internal node, node_id_cnt))
+      Ok (st2, (Betree_Node_Internal node, node_id_cnt))
   | Betree_Node_Leaf node ->
     let* (st1, content) = betree_load_leaf_node node.id st in
     let* content1 = betree_Node_apply_messages_to_leaf content msgs in
@@ -585,10 +585,10 @@ and betree_Node_apply_messages
       let* (st2, (new_node, node_id_cnt1)) =
         betree_Leaf_split node content1 params node_id_cnt st1 in
       let* (st3, _) = betree_store_leaf_node node.id Betree_List_Nil st2 in
-      Return (st3, (Betree_Node_Internal new_node, node_id_cnt1))
+      Ok (st3, (Betree_Node_Internal new_node, node_id_cnt1))
     else
       let* (st2, _) = betree_store_leaf_node node.id content1 st1 in
-      Return (st2, (Betree_Node_Leaf { node with size = len }, node_id_cnt))
+      Ok (st2, (Betree_Node_Leaf { node with size = len }, node_id_cnt))
   end
 
 (** [betree_main::betree::{betree_main::betree::Node#5}::apply]:
@@ -603,7 +603,7 @@ let betree_Node_apply
     betree_Node_apply_messages self params node_id_cnt (Betree_List_Cons (key,
       new_msg) Betree_List_Nil) st in
   let (self1, node_id_cnt1) = p in
-  Return (st1, (self1, node_id_cnt1))
+  Ok (st1, (self1, node_id_cnt1))
 
 (** [betree_main::betree::{betree_main::betree::BeTree#6}::new]:
     Source: 'src/betree.rs', lines 849:4-849:60 *)
@@ -614,7 +614,7 @@ let betree_BeTree_new
   let* node_id_cnt = betree_NodeIdCounter_new in
   let* (id, node_id_cnt1) = betree_NodeIdCounter_fresh_id node_id_cnt in
   let* (st1, _) = betree_store_leaf_node id Betree_List_Nil st in
-  Return (st1,
+  Ok (st1,
     {
       params = { min_flush_size = min_flush_size; split_size = split_size };
       node_id_cnt = node_id_cnt1;
@@ -630,7 +630,7 @@ let betree_BeTree_apply
   let* (st1, p) =
     betree_Node_apply self.root self.params self.node_id_cnt key msg st in
   let (n, nic) = p in
-  Return (st1, { self with node_id_cnt = nic; root = n })
+  Ok (st1, { self with node_id_cnt = nic; root = n })
 
 (** [betree_main::betree::{betree_main::betree::BeTree#6}::insert]:
     Source: 'src/betree.rs', lines 874:4-874:52 *)
@@ -664,13 +664,13 @@ let betree_BeTree_lookup
   result (state & ((option u64) & betree_BeTree_t))
   =
   let* (st1, (o, n)) = betree_Node_lookup self.root key st in
-  Return (st1, (o, { self with root = n }))
+  Ok (st1, (o, { self with root = n }))
 
 (** [betree_main::main]:
     Source: 'src/betree_main.rs', lines 5:0-5:9 *)
 let main : result unit =
-  Return ()
+  Ok ()
 
 (** Unit test for [betree_main::main] *)
-let _ = assert_norm (main = Return ())
+let _ = assert_norm (main = Ok ())
 
diff --git a/tests/fstar/betree_back_stateful/Primitives.fst b/tests/fstar/betree_back_stateful/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/betree_back_stateful/Primitives.fst
+++ b/tests/fstar/betree_back_stateful/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/demo/Demo.fst b/tests/fstar/demo/Demo.fst
index 9c59ab9b..b210662f 100644
--- a/tests/fstar/demo/Demo.fst
+++ b/tests/fstar/demo/Demo.fst
@@ -10,8 +10,8 @@ open Primitives
 let choose
   (t : Type0) (b : bool) (x : t) (y : t) : result (t & (t -> result (t & t))) =
   if b
-  then let back = fun ret -> Return (ret, y) in Return (x, back)
-  else let back = fun ret -> Return (x, ret) in Return (y, back)
+  then let back = fun ret -> Ok (ret, y) in Ok (x, back)
+  else let back = fun ret -> Ok (x, ret) in Ok (y, back)
 
 (** [demo::mul2_add1]:
     Source: 'src/demo.rs', lines 13:0-13:31 *)
@@ -31,7 +31,7 @@ let incr (x : u32) : result u32 =
 (** [demo::use_incr]:
     Source: 'src/demo.rs', lines 25:0-25:17 *)
 let use_incr : result unit =
-  let* x = incr 0 in let* x1 = incr x in let* _ = incr x1 in Return ()
+  let* x = incr 0 in let* x1 = incr x in let* _ = incr x1 in Ok ()
 
 (** [demo::CList]
     Source: 'src/demo.rs', lines 34:0-34:17 *)
@@ -48,7 +48,7 @@ let rec list_nth (t : Type0) (n : nat) (l : cList_t t) (i : u32) : result t =
     let n1 = decrease n in
     begin match l with
     | CList_CCons x tl ->
-      if i = 0 then Return x else let* i1 = u32_sub i 1 in list_nth t n1 tl i1
+      if i = 0 then Ok x else let* i1 = u32_sub i 1 in list_nth t n1 tl i1
     | CList_CNil -> Fail Failure
     end
 
@@ -65,15 +65,14 @@ let rec list_nth_mut
     begin match l with
     | CList_CCons x tl ->
       if i = 0
-      then
-        let back = fun ret -> Return (CList_CCons ret tl) in Return (x, back)
+      then let back = fun ret -> Ok (CList_CCons ret tl) in Ok (x, back)
       else
         let* i1 = u32_sub i 1 in
         let* (x1, list_nth_mut_back) = list_nth_mut t n1 tl i1 in
         let back =
-          fun ret ->
-            let* tl1 = list_nth_mut_back ret in Return (CList_CCons x tl1) in
-        Return (x1, back)
+          fun ret -> let* tl1 = list_nth_mut_back ret in Ok (CList_CCons x tl1)
+          in
+        Ok (x1, back)
     | CList_CNil -> Fail Failure
     end
 
@@ -90,14 +89,12 @@ let rec list_nth_mut1_loop
     begin match l with
     | CList_CCons x tl ->
       if i = 0
-      then
-        let back = fun ret -> Return (CList_CCons ret tl) in Return (x, back)
+      then let back = fun ret -> Ok (CList_CCons ret tl) in Ok (x, back)
       else
         let* i1 = u32_sub i 1 in
         let* (x1, back) = list_nth_mut1_loop t n1 tl i1 in
-        let back1 =
-          fun ret -> let* tl1 = back ret in Return (CList_CCons x tl1) in
-        Return (x1, back1)
+        let back1 = fun ret -> let* tl1 = back ret in Ok (CList_CCons x tl1) in
+        Ok (x1, back1)
     | CList_CNil -> Fail Failure
     end
 
@@ -117,7 +114,7 @@ let rec i32_id (n : nat) (i : i32) : result i32 =
   else
     let n1 = decrease n in
     if i = 0
-    then Return 0
+    then Ok 0
     else let* i1 = i32_sub i 1 in let* i2 = i32_id n1 i1 in i32_add i2 1
 
 (** [demo::list_tail]:
@@ -134,10 +131,9 @@ let rec list_tail
     | CList_CCons x tl ->
       let* (c, list_tail_back) = list_tail t n1 tl in
       let back =
-        fun ret -> let* tl1 = list_tail_back ret in Return (CList_CCons x tl1)
-        in
-      Return (c, back)
-    | CList_CNil -> Return (CList_CNil, Return)
+        fun ret -> let* tl1 = list_tail_back ret in Ok (CList_CCons x tl1) in
+      Ok (c, back)
+    | CList_CNil -> Ok (CList_CNil, Ok)
     end
 
 (** Trait declaration: [demo::Counter]
@@ -147,7 +143,7 @@ noeq type counter_t (self : Type0) = { incr : self -> result (usize & self); }
 (** [demo::{(demo::Counter for usize)}::incr]:
     Source: 'src/demo.rs', lines 102:4-102:31 *)
 let counterUsize_incr (self : usize) : result (usize & usize) =
-  let* self1 = usize_add self 1 in Return (self, self1)
+  let* self1 = usize_add self 1 in Ok (self, self1)
 
 (** Trait implementation: [demo::{(demo::Counter for usize)}]
     Source: 'src/demo.rs', lines 101:0-101:22 *)
diff --git a/tests/fstar/demo/Primitives.fst b/tests/fstar/demo/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/demo/Primitives.fst
+++ b/tests/fstar/demo/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/hashmap/Hashmap.Funs.fst b/tests/fstar/hashmap/Hashmap.Funs.fst
index d897933a..2be587af 100644
--- a/tests/fstar/hashmap/Hashmap.Funs.fst
+++ b/tests/fstar/hashmap/Hashmap.Funs.fst
@@ -10,7 +10,7 @@ include Hashmap.Clauses
 (** [hashmap::hash_key]:
     Source: 'src/hashmap.rs', lines 27:0-27:32 *)
 let hash_key (k : usize) : result usize =
-  Return k
+  Ok k
 
 (** [hashmap::{hashmap::HashMap<T>}::allocate_slots]: loop 0:
     Source: 'src/hashmap.rs', lines 50:4-56:5 *)
@@ -24,7 +24,7 @@ let rec hashMap_allocate_slots_loop
     let* slots1 = alloc_vec_Vec_push (list_t t) slots List_Nil in
     let* n1 = usize_sub n 1 in
     hashMap_allocate_slots_loop t slots1 n1
-  else Return slots
+  else Ok slots
 
 (** [hashmap::{hashmap::HashMap<T>}::allocate_slots]:
     Source: 'src/hashmap.rs', lines 50:4-50:76 *)
@@ -45,7 +45,7 @@ let hashMap_new_with_capacity
     in
   let* i = usize_mul capacity max_load_dividend in
   let* i1 = usize_div i max_load_divisor in
-  Return
+  Ok
     {
       num_entries = 0;
       max_load_factor = (max_load_dividend, max_load_divisor);
@@ -74,18 +74,18 @@ let rec hashMap_clear_loop
     let* i2 = usize_add i 1 in
     let* slots1 = index_mut_back List_Nil in
     hashMap_clear_loop t slots1 i2
-  else Return slots
+  else Ok slots
 
 (** [hashmap::{hashmap::HashMap<T>}::clear]:
     Source: 'src/hashmap.rs', lines 80:4-80:27 *)
 let hashMap_clear (t : Type0) (self : hashMap_t t) : result (hashMap_t t) =
   let* hm = hashMap_clear_loop t self.slots 0 in
-  Return { self with num_entries = 0; slots = hm }
+  Ok { self with num_entries = 0; slots = hm }
 
 (** [hashmap::{hashmap::HashMap<T>}::len]:
     Source: 'src/hashmap.rs', lines 90:4-90:30 *)
 let hashMap_len (t : Type0) (self : hashMap_t t) : result usize =
-  Return self.num_entries
+  Ok self.num_entries
 
 (** [hashmap::{hashmap::HashMap<T>}::insert_in_list]: loop 0:
     Source: 'src/hashmap.rs', lines 97:4-114:5 *)
@@ -97,11 +97,11 @@ let rec hashMap_insert_in_list_loop
   begin match ls with
   | List_Cons ckey cvalue tl ->
     if ckey = key
-    then Return (false, List_Cons ckey value tl)
+    then Ok (false, List_Cons ckey value tl)
     else
       let* (b, tl1) = hashMap_insert_in_list_loop t key value tl in
-      Return (b, List_Cons ckey cvalue tl1)
-  | List_Nil -> Return (true, List_Cons key value List_Nil)
+      Ok (b, List_Cons ckey cvalue tl1)
+  | List_Nil -> Ok (true, List_Cons key value List_Nil)
   end
 
 (** [hashmap::{hashmap::HashMap<T>}::insert_in_list]:
@@ -130,8 +130,8 @@ let hashMap_insert_no_resize
   then
     let* i1 = usize_add self.num_entries 1 in
     let* v = index_mut_back l1 in
-    Return { self with num_entries = i1; slots = v }
-  else let* v = index_mut_back l1 in Return { self with slots = v }
+    Ok { self with num_entries = i1; slots = v }
+  else let* v = index_mut_back l1 in Ok { self with slots = v }
 
 (** [hashmap::{hashmap::HashMap<T>}::move_elements_from_list]: loop 0:
     Source: 'src/hashmap.rs', lines 183:4-196:5 *)
@@ -144,7 +144,7 @@ let rec hashMap_move_elements_from_list_loop
   | List_Cons k v tl ->
     let* ntable1 = hashMap_insert_no_resize t ntable k v in
     hashMap_move_elements_from_list_loop t ntable1 tl
-  | List_Nil -> Return ntable
+  | List_Nil -> Ok ntable
   end
 
 (** [hashmap::{hashmap::HashMap<T>}::move_elements_from_list]:
@@ -172,7 +172,7 @@ let rec hashMap_move_elements_loop
     let* i2 = usize_add i 1 in
     let* slots1 = index_mut_back l1 in
     hashMap_move_elements_loop t ntable1 slots1 i2
-  else Return (ntable, slots)
+  else Ok (ntable, slots)
 
 (** [hashmap::{hashmap::HashMap<T>}::move_elements]:
     Source: 'src/hashmap.rs', lines 171:4-171:95 *)
@@ -198,10 +198,10 @@ let hashMap_try_resize
     let* ntable = hashMap_new_with_capacity t i3 i i1 in
     let* p = hashMap_move_elements t ntable self.slots 0 in
     let (ntable1, _) = p in
-    Return
+    Ok
       { ntable1 with num_entries = self.num_entries; max_load_factor = (i, i1)
       }
-  else Return { self with max_load_factor = (i, i1) }
+  else Ok { self with max_load_factor = (i, i1) }
 
 (** [hashmap::{hashmap::HashMap<T>}::insert]:
     Source: 'src/hashmap.rs', lines 129:4-129:48 *)
@@ -211,7 +211,7 @@ let hashMap_insert
   =
   let* self1 = hashMap_insert_no_resize t self key value in
   let* i = hashMap_len t self1 in
-  if i > self1.max_load then hashMap_try_resize t self1 else Return self1
+  if i > self1.max_load then hashMap_try_resize t self1 else Ok self1
 
 (** [hashmap::{hashmap::HashMap<T>}::contains_key_in_list]: loop 0:
     Source: 'src/hashmap.rs', lines 206:4-219:5 *)
@@ -222,10 +222,8 @@ let rec hashMap_contains_key_in_list_loop
   =
   begin match ls with
   | List_Cons ckey _ tl ->
-    if ckey = key
-    then Return true
-    else hashMap_contains_key_in_list_loop t key tl
-  | List_Nil -> Return false
+    if ckey = key then Ok true else hashMap_contains_key_in_list_loop t key tl
+  | List_Nil -> Ok false
   end
 
 (** [hashmap::{hashmap::HashMap<T>}::contains_key_in_list]:
@@ -255,7 +253,7 @@ let rec hashMap_get_in_list_loop
   =
   begin match ls with
   | List_Cons ckey cvalue tl ->
-    if ckey = key then Return cvalue else hashMap_get_in_list_loop t key tl
+    if ckey = key then Ok cvalue else hashMap_get_in_list_loop t key tl
   | List_Nil -> Fail Failure
   end
 
@@ -286,14 +284,12 @@ let rec hashMap_get_mut_in_list_loop
   begin match ls with
   | List_Cons ckey cvalue tl ->
     if ckey = key
-    then
-      let back = fun ret -> Return (List_Cons ckey ret tl) in
-      Return (cvalue, back)
+    then let back = fun ret -> Ok (List_Cons ckey ret tl) in Ok (cvalue, back)
     else
       let* (x, back) = hashMap_get_mut_in_list_loop t tl key in
       let back1 =
-        fun ret -> let* tl1 = back ret in Return (List_Cons ckey cvalue tl1) in
-      Return (x, back1)
+        fun ret -> let* tl1 = back ret in Ok (List_Cons ckey cvalue tl1) in
+      Ok (x, back1)
   | List_Nil -> Fail Failure
   end
 
@@ -323,8 +319,8 @@ let hashMap_get_mut
     fun ret ->
       let* l1 = get_mut_in_list_back ret in
       let* v = index_mut_back l1 in
-      Return { self with slots = v } in
-  Return (x, back)
+      Ok { self with slots = v } in
+  Ok (x, back)
 
 (** [hashmap::{hashmap::HashMap<T>}::remove_from_list]: loop 0:
     Source: 'src/hashmap.rs', lines 265:4-291:5 *)
@@ -340,13 +336,13 @@ let rec hashMap_remove_from_list_loop
       let (mv_ls, _) =
         core_mem_replace (list_t t) (List_Cons ckey x tl) List_Nil in
       begin match mv_ls with
-      | List_Cons _ cvalue tl1 -> Return (Some cvalue, tl1)
+      | List_Cons _ cvalue tl1 -> Ok (Some cvalue, tl1)
       | List_Nil -> Fail Failure
       end
     else
       let* (o, tl1) = hashMap_remove_from_list_loop t key tl in
-      Return (o, List_Cons ckey x tl1)
-  | List_Nil -> Return (None, List_Nil)
+      Ok (o, List_Cons ckey x tl1)
+  | List_Nil -> Ok (None, List_Nil)
   end
 
 (** [hashmap::{hashmap::HashMap<T>}::remove_from_list]:
@@ -372,12 +368,11 @@ let hashMap_remove
       hash_mod in
   let* (x, l1) = hashMap_remove_from_list t key l in
   begin match x with
-  | None ->
-    let* v = index_mut_back l1 in Return (None, { self with slots = v })
+  | None -> let* v = index_mut_back l1 in Ok (None, { self with slots = v })
   | Some x1 ->
     let* i1 = usize_sub self.num_entries 1 in
     let* v = index_mut_back l1 in
-    Return (Some x1, { self with num_entries = i1; slots = v })
+    Ok (Some x1, { self with num_entries = i1; slots = v })
   end
 
 (** [hashmap::test1]:
@@ -414,6 +409,6 @@ let test1 : result unit =
             then Fail Failure
             else
               let* i4 = hashMap_get u64 hm6 1056 in
-              if not (i4 = 256) then Fail Failure else Return ()
+              if not (i4 = 256) then Fail Failure else Ok ()
       end
 
diff --git a/tests/fstar/hashmap/Primitives.fst b/tests/fstar/hashmap/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/hashmap/Primitives.fst
+++ b/tests/fstar/hashmap/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/hashmap_on_disk/HashmapMain.Funs.fst b/tests/fstar/hashmap_on_disk/HashmapMain.Funs.fst
index e0005c81..ff86e087 100644
--- a/tests/fstar/hashmap_on_disk/HashmapMain.Funs.fst
+++ b/tests/fstar/hashmap_on_disk/HashmapMain.Funs.fst
@@ -11,7 +11,7 @@ include HashmapMain.Clauses
 (** [hashmap_main::hashmap::hash_key]:
     Source: 'src/hashmap.rs', lines 27:0-27:32 *)
 let hashmap_hash_key (k : usize) : result usize =
-  Return k
+  Ok k
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::allocate_slots]: loop 0:
     Source: 'src/hashmap.rs', lines 50:4-56:5 *)
@@ -26,7 +26,7 @@ let rec hashmap_HashMap_allocate_slots_loop
       in
     let* n1 = usize_sub n 1 in
     hashmap_HashMap_allocate_slots_loop t slots1 n1
-  else Return slots
+  else Ok slots
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::allocate_slots]:
     Source: 'src/hashmap.rs', lines 50:4-50:76 *)
@@ -48,7 +48,7 @@ let hashmap_HashMap_new_with_capacity
       capacity in
   let* i = usize_mul capacity max_load_dividend in
   let* i1 = usize_div i max_load_divisor in
-  Return
+  Ok
     {
       num_entries = 0;
       max_load_factor = (max_load_dividend, max_load_divisor);
@@ -78,20 +78,20 @@ let rec hashmap_HashMap_clear_loop
     let* i2 = usize_add i 1 in
     let* slots1 = index_mut_back Hashmap_List_Nil in
     hashmap_HashMap_clear_loop t slots1 i2
-  else Return slots
+  else Ok slots
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::clear]:
     Source: 'src/hashmap.rs', lines 80:4-80:27 *)
 let hashmap_HashMap_clear
   (t : Type0) (self : hashmap_HashMap_t t) : result (hashmap_HashMap_t t) =
   let* hm = hashmap_HashMap_clear_loop t self.slots 0 in
-  Return { self with num_entries = 0; slots = hm }
+  Ok { self with num_entries = 0; slots = hm }
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::len]:
     Source: 'src/hashmap.rs', lines 90:4-90:30 *)
 let hashmap_HashMap_len
   (t : Type0) (self : hashmap_HashMap_t t) : result usize =
-  Return self.num_entries
+  Ok self.num_entries
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::insert_in_list]: loop 0:
     Source: 'src/hashmap.rs', lines 97:4-114:5 *)
@@ -103,12 +103,11 @@ let rec hashmap_HashMap_insert_in_list_loop
   begin match ls with
   | Hashmap_List_Cons ckey cvalue tl ->
     if ckey = key
-    then Return (false, Hashmap_List_Cons ckey value tl)
+    then Ok (false, Hashmap_List_Cons ckey value tl)
     else
       let* (b, tl1) = hashmap_HashMap_insert_in_list_loop t key value tl in
-      Return (b, Hashmap_List_Cons ckey cvalue tl1)
-  | Hashmap_List_Nil ->
-    Return (true, Hashmap_List_Cons key value Hashmap_List_Nil)
+      Ok (b, Hashmap_List_Cons ckey cvalue tl1)
+  | Hashmap_List_Nil -> Ok (true, Hashmap_List_Cons key value Hashmap_List_Nil)
   end
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::insert_in_list]:
@@ -137,8 +136,8 @@ let hashmap_HashMap_insert_no_resize
   then
     let* i1 = usize_add self.num_entries 1 in
     let* v = index_mut_back l1 in
-    Return { self with num_entries = i1; slots = v }
-  else let* v = index_mut_back l1 in Return { self with slots = v }
+    Ok { self with num_entries = i1; slots = v }
+  else let* v = index_mut_back l1 in Ok { self with slots = v }
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::move_elements_from_list]: loop 0:
     Source: 'src/hashmap.rs', lines 183:4-196:5 *)
@@ -152,7 +151,7 @@ let rec hashmap_HashMap_move_elements_from_list_loop
   | Hashmap_List_Cons k v tl ->
     let* ntable1 = hashmap_HashMap_insert_no_resize t ntable k v in
     hashmap_HashMap_move_elements_from_list_loop t ntable1 tl
-  | Hashmap_List_Nil -> Return ntable
+  | Hashmap_List_Nil -> Ok ntable
   end
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::move_elements_from_list]:
@@ -183,7 +182,7 @@ let rec hashmap_HashMap_move_elements_loop
     let* i2 = usize_add i 1 in
     let* slots1 = index_mut_back l1 in
     hashmap_HashMap_move_elements_loop t ntable1 slots1 i2
-  else Return (ntable, slots)
+  else Ok (ntable, slots)
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::move_elements]:
     Source: 'src/hashmap.rs', lines 171:4-171:95 *)
@@ -209,10 +208,10 @@ let hashmap_HashMap_try_resize
     let* ntable = hashmap_HashMap_new_with_capacity t i3 i i1 in
     let* p = hashmap_HashMap_move_elements t ntable self.slots 0 in
     let (ntable1, _) = p in
-    Return
+    Ok
       { ntable1 with num_entries = self.num_entries; max_load_factor = (i, i1)
       }
-  else Return { self with max_load_factor = (i, i1) }
+  else Ok { self with max_load_factor = (i, i1) }
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::insert]:
     Source: 'src/hashmap.rs', lines 129:4-129:48 *)
@@ -222,9 +221,7 @@ let hashmap_HashMap_insert
   =
   let* self1 = hashmap_HashMap_insert_no_resize t self key value in
   let* i = hashmap_HashMap_len t self1 in
-  if i > self1.max_load
-  then hashmap_HashMap_try_resize t self1
-  else Return self1
+  if i > self1.max_load then hashmap_HashMap_try_resize t self1 else Ok self1
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::contains_key_in_list]: loop 0:
     Source: 'src/hashmap.rs', lines 206:4-219:5 *)
@@ -236,9 +233,9 @@ let rec hashmap_HashMap_contains_key_in_list_loop
   begin match ls with
   | Hashmap_List_Cons ckey _ tl ->
     if ckey = key
-    then Return true
+    then Ok true
     else hashmap_HashMap_contains_key_in_list_loop t key tl
-  | Hashmap_List_Nil -> Return false
+  | Hashmap_List_Nil -> Ok false
   end
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::contains_key_in_list]:
@@ -269,9 +266,7 @@ let rec hashmap_HashMap_get_in_list_loop
   =
   begin match ls with
   | Hashmap_List_Cons ckey cvalue tl ->
-    if ckey = key
-    then Return cvalue
-    else hashmap_HashMap_get_in_list_loop t key tl
+    if ckey = key then Ok cvalue else hashmap_HashMap_get_in_list_loop t key tl
   | Hashmap_List_Nil -> Fail Failure
   end
 
@@ -305,14 +300,14 @@ let rec hashmap_HashMap_get_mut_in_list_loop
   | Hashmap_List_Cons ckey cvalue tl ->
     if ckey = key
     then
-      let back = fun ret -> Return (Hashmap_List_Cons ckey ret tl) in
-      Return (cvalue, back)
+      let back = fun ret -> Ok (Hashmap_List_Cons ckey ret tl) in
+      Ok (cvalue, back)
     else
       let* (x, back) = hashmap_HashMap_get_mut_in_list_loop t tl key in
       let back1 =
         fun ret ->
-          let* tl1 = back ret in Return (Hashmap_List_Cons ckey cvalue tl1) in
-      Return (x, back1)
+          let* tl1 = back ret in Ok (Hashmap_List_Cons ckey cvalue tl1) in
+      Ok (x, back1)
   | Hashmap_List_Nil -> Fail Failure
   end
 
@@ -342,8 +337,8 @@ let hashmap_HashMap_get_mut
     fun ret ->
       let* l1 = get_mut_in_list_back ret in
       let* v = index_mut_back l1 in
-      Return { self with slots = v } in
-  Return (x, back)
+      Ok { self with slots = v } in
+  Ok (x, back)
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::remove_from_list]: loop 0:
     Source: 'src/hashmap.rs', lines 265:4-291:5 *)
@@ -360,13 +355,13 @@ let rec hashmap_HashMap_remove_from_list_loop
         core_mem_replace (hashmap_List_t t) (Hashmap_List_Cons ckey x tl)
           Hashmap_List_Nil in
       begin match mv_ls with
-      | Hashmap_List_Cons _ cvalue tl1 -> Return (Some cvalue, tl1)
+      | Hashmap_List_Cons _ cvalue tl1 -> Ok (Some cvalue, tl1)
       | Hashmap_List_Nil -> Fail Failure
       end
     else
       let* (o, tl1) = hashmap_HashMap_remove_from_list_loop t key tl in
-      Return (o, Hashmap_List_Cons ckey x tl1)
-  | Hashmap_List_Nil -> Return (None, Hashmap_List_Nil)
+      Ok (o, Hashmap_List_Cons ckey x tl1)
+  | Hashmap_List_Nil -> Ok (None, Hashmap_List_Nil)
   end
 
 (** [hashmap_main::hashmap::{hashmap_main::hashmap::HashMap<T>}::remove_from_list]:
@@ -392,12 +387,11 @@ let hashmap_HashMap_remove
       self.slots hash_mod in
   let* (x, l1) = hashmap_HashMap_remove_from_list t key l in
   begin match x with
-  | None ->
-    let* v = index_mut_back l1 in Return (None, { self with slots = v })
+  | None -> let* v = index_mut_back l1 in Ok (None, { self with slots = v })
   | Some x1 ->
     let* i1 = usize_sub self.num_entries 1 in
     let* v = index_mut_back l1 in
-    Return (Some x1, { self with num_entries = i1; slots = v })
+    Ok (Some x1, { self with num_entries = i1; slots = v })
   end
 
 (** [hashmap_main::hashmap::test1]:
@@ -434,7 +428,7 @@ let hashmap_test1 : result unit =
             then Fail Failure
             else
               let* i4 = hashmap_HashMap_get u64 hm6 1056 in
-              if not (i4 = 256) then Fail Failure else Return ()
+              if not (i4 = 256) then Fail Failure else Ok ()
       end
 
 (** [hashmap_main::insert_on_disk]:
@@ -448,5 +442,5 @@ let insert_on_disk
 (** [hashmap_main::main]:
     Source: 'src/hashmap_main.rs', lines 16:0-16:13 *)
 let main : result unit =
-  Return ()
+  Ok ()
 
diff --git a/tests/fstar/hashmap_on_disk/Primitives.fst b/tests/fstar/hashmap_on_disk/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/hashmap_on_disk/Primitives.fst
+++ b/tests/fstar/hashmap_on_disk/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/misc/Bitwise.fst b/tests/fstar/misc/Bitwise.fst
index 7330f07a..11ef6861 100644
--- a/tests/fstar/misc/Bitwise.fst
+++ b/tests/fstar/misc/Bitwise.fst
@@ -18,15 +18,15 @@ let shift_i32 (a : i32) : result i32 =
 (** [bitwise::xor_u32]:
     Source: 'src/bitwise.rs', lines 17:0-17:37 *)
 let xor_u32 (a : u32) (b : u32) : result u32 =
-  Return (u32_xor a b)
+  Ok (u32_xor a b)
 
 (** [bitwise::or_u32]:
     Source: 'src/bitwise.rs', lines 21:0-21:36 *)
 let or_u32 (a : u32) (b : u32) : result u32 =
-  Return (u32_or a b)
+  Ok (u32_or a b)
 
 (** [bitwise::and_u32]:
     Source: 'src/bitwise.rs', lines 25:0-25:37 *)
 let and_u32 (a : u32) (b : u32) : result u32 =
-  Return (u32_and a b)
+  Ok (u32_and a b)
 
diff --git a/tests/fstar/misc/Constants.fst b/tests/fstar/misc/Constants.fst
index 8d1cf3ce..4fbafb83 100644
--- a/tests/fstar/misc/Constants.fst
+++ b/tests/fstar/misc/Constants.fst
@@ -7,17 +7,17 @@ open Primitives
 
 (** [constants::X0]
     Source: 'src/constants.rs', lines 5:0-5:17 *)
-let x0_body : result u32 = Return 0
+let x0_body : result u32 = Ok 0
 let x0 : u32 = eval_global x0_body
 
 (** [constants::X1]
     Source: 'src/constants.rs', lines 7:0-7:17 *)
-let x1_body : result u32 = Return core_u32_max
+let x1_body : result u32 = Ok core_u32_max
 let x1 : u32 = eval_global x1_body
 
 (** [constants::X2]
     Source: 'src/constants.rs', lines 10:0-10:17 *)
-let x2_body : result u32 = Return 3
+let x2_body : result u32 = Ok 3
 let x2 : u32 = eval_global x2_body
 
 (** [constants::incr]:
@@ -33,7 +33,7 @@ let x3 : u32 = eval_global x3_body
 (** [constants::mk_pair0]:
     Source: 'src/constants.rs', lines 23:0-23:51 *)
 let mk_pair0 (x : u32) (y1 : u32) : result (u32 & u32) =
-  Return (x, y1)
+  Ok (x, y1)
 
 (** [constants::Pair]
     Source: 'src/constants.rs', lines 36:0-36:23 *)
@@ -42,7 +42,7 @@ type pair_t (t1 t2 : Type0) = { x : t1; y : t2; }
 (** [constants::mk_pair1]:
     Source: 'src/constants.rs', lines 27:0-27:55 *)
 let mk_pair1 (x : u32) (y1 : u32) : result (pair_t u32 u32) =
-  Return { x = x; y = y1 }
+  Ok { x = x; y = y1 }
 
 (** [constants::P0]
     Source: 'src/constants.rs', lines 31:0-31:24 *)
@@ -56,12 +56,12 @@ let p1 : pair_t u32 u32 = eval_global p1_body
 
 (** [constants::P2]
     Source: 'src/constants.rs', lines 33:0-33:24 *)
-let p2_body : result (u32 & u32) = Return (0, 1)
+let p2_body : result (u32 & u32) = Ok (0, 1)
 let p2 : (u32 & u32) = eval_global p2_body
 
 (** [constants::P3]
     Source: 'src/constants.rs', lines 34:0-34:28 *)
-let p3_body : result (pair_t u32 u32) = Return { x = 0; y = 1 }
+let p3_body : result (pair_t u32 u32) = Ok { x = 0; y = 1 }
 let p3 : pair_t u32 u32 = eval_global p3_body
 
 (** [constants::Wrap]
@@ -71,7 +71,7 @@ type wrap_t (t : Type0) = { value : t; }
 (** [constants::{constants::Wrap<T>}::new]:
     Source: 'src/constants.rs', lines 54:4-54:41 *)
 let wrap_new (t : Type0) (value : t) : result (wrap_t t) =
-  Return { value = value }
+  Ok { value = value }
 
 (** [constants::Y]
     Source: 'src/constants.rs', lines 41:0-41:22 *)
@@ -81,7 +81,7 @@ let y : wrap_t i32 = eval_global y_body
 (** [constants::unwrap_y]:
     Source: 'src/constants.rs', lines 43:0-43:30 *)
 let unwrap_y : result i32 =
-  Return y.value
+  Ok y.value
 
 (** [constants::YVAL]
     Source: 'src/constants.rs', lines 47:0-47:19 *)
@@ -90,13 +90,13 @@ let yval : i32 = eval_global yval_body
 
 (** [constants::get_z1::Z1]
     Source: 'src/constants.rs', lines 62:4-62:17 *)
-let get_z1_z1_body : result i32 = Return 3
+let get_z1_z1_body : result i32 = Ok 3
 let get_z1_z1 : i32 = eval_global get_z1_z1_body
 
 (** [constants::get_z1]:
     Source: 'src/constants.rs', lines 61:0-61:28 *)
 let get_z1 : result i32 =
-  Return get_z1_z1
+  Ok get_z1_z1
 
 (** [constants::add]:
     Source: 'src/constants.rs', lines 66:0-66:39 *)
@@ -105,12 +105,12 @@ let add (a : i32) (b : i32) : result i32 =
 
 (** [constants::Q1]
     Source: 'src/constants.rs', lines 74:0-74:17 *)
-let q1_body : result i32 = Return 5
+let q1_body : result i32 = Ok 5
 let q1 : i32 = eval_global q1_body
 
 (** [constants::Q2]
     Source: 'src/constants.rs', lines 75:0-75:17 *)
-let q2_body : result i32 = Return q1
+let q2_body : result i32 = Ok q1
 let q2 : i32 = eval_global q2_body
 
 (** [constants::Q3]
@@ -125,7 +125,7 @@ let get_z2 : result i32 =
 
 (** [constants::S1]
     Source: 'src/constants.rs', lines 80:0-80:18 *)
-let s1_body : result u32 = Return 6
+let s1_body : result u32 = Ok 6
 let s1 : u32 = eval_global s1_body
 
 (** [constants::S2]
@@ -135,7 +135,7 @@ let s2 : u32 = eval_global s2_body
 
 (** [constants::S3]
     Source: 'src/constants.rs', lines 82:0-82:29 *)
-let s3_body : result (pair_t u32 u32) = Return p3
+let s3_body : result (pair_t u32 u32) = Ok p3
 let s3 : pair_t u32 u32 = eval_global s3_body
 
 (** [constants::S4]
@@ -149,11 +149,11 @@ type v_t (t : Type0) (n : usize) = { x : array t n; }
 
 (** [constants::{constants::V<T, N>#1}::LEN]
     Source: 'src/constants.rs', lines 91:4-91:24 *)
-let v_len_body (t : Type0) (n : usize) : result usize = Return n
+let v_len_body (t : Type0) (n : usize) : result usize = Ok n
 let v_len (t : Type0) (n : usize) : usize = eval_global (v_len_body t n)
 
 (** [constants::use_v]:
     Source: 'src/constants.rs', lines 94:0-94:42 *)
 let use_v (t : Type0) (n : usize) : result usize =
-  Return (v_len t n)
+  Ok (v_len t n)
 
diff --git a/tests/fstar/misc/External.Funs.fst b/tests/fstar/misc/External.Funs.fst
index 78960404..d4247b8f 100644
--- a/tests/fstar/misc/External.Funs.fst
+++ b/tests/fstar/misc/External.Funs.fst
@@ -22,10 +22,10 @@ let test_new_non_zero_u32
 (** [external::test_vec]:
     Source: 'src/external.rs', lines 17:0-17:17 *)
 let test_vec : result unit =
-  let* _ = alloc_vec_Vec_push u32 (alloc_vec_Vec_new u32) 0 in Return ()
+  let* _ = alloc_vec_Vec_push u32 (alloc_vec_Vec_new u32) 0 in Ok ()
 
 (** Unit test for [external::test_vec] *)
-let _ = assert_norm (test_vec = Return ())
+let _ = assert_norm (test_vec = Ok ())
 
 (** [external::custom_swap]:
     Source: 'src/external.rs', lines 24:0-24:66 *)
@@ -34,8 +34,8 @@ let custom_swap
   result (state & (t & (t -> state -> result (state & (t & t)))))
   =
   let* (st1, (x1, y1)) = core_mem_swap t x y st in
-  let back = fun ret st2 -> Return (st2, (ret, y1)) in
-  Return (st1, (x1, back))
+  let back = fun ret st2 -> Ok (st2, (ret, y1)) in
+  Ok (st1, (x1, back))
 
 (** [external::test_custom_swap]:
     Source: 'src/external.rs', lines 29:0-29:59 *)
@@ -43,12 +43,12 @@ let test_custom_swap
   (x : u32) (y : u32) (st : state) : result (state & (u32 & u32)) =
   let* (st1, (_, custom_swap_back)) = custom_swap u32 x y st in
   let* (_, (x1, y1)) = custom_swap_back 1 st1 in
-  Return (st1, (x1, y1))
+  Ok (st1, (x1, y1))
 
 (** [external::test_swap_non_zero]:
     Source: 'src/external.rs', lines 35:0-35:44 *)
 let test_swap_non_zero (x : u32) (st : state) : result (state & u32) =
   let* (st1, p) = swap u32 x 0 st in
   let (x1, _) = p in
-  if x1 = 0 then Fail Failure else Return (st1, x1)
+  if x1 = 0 then Fail Failure else Ok (st1, x1)
 
diff --git a/tests/fstar/misc/Loops.Funs.fst b/tests/fstar/misc/Loops.Funs.fst
index 93683deb..26cb91d2 100644
--- a/tests/fstar/misc/Loops.Funs.fst
+++ b/tests/fstar/misc/Loops.Funs.fst
@@ -70,7 +70,7 @@ let rec sum_array_loop
     let* s1 = u32_add s i1 in
     let* i2 = usize_add i 1 in
     sum_array_loop n a i2 s1
-  else Return s
+  else Ok s
 
 (** [loops::sum_array]:
     Source: 'src/loops.rs', lines 50:0-50:52 *)
@@ -92,7 +92,7 @@ let rec clear_loop
     let* i2 = usize_add i 1 in
     let* v1 = index_mut_back 0 in
     clear_loop v1 i2
-  else Return v
+  else Ok v
 
 (** [loops::clear]:
     Source: 'src/loops.rs', lines 62:0-62:30 *)
@@ -106,8 +106,8 @@ let rec list_mem_loop
   Tot (result bool) (decreases (list_mem_loop_decreases x ls))
   =
   begin match ls with
-  | List_Cons y tl -> if y = x then Return true else list_mem_loop x tl
-  | List_Nil -> Return false
+  | List_Cons y tl -> if y = x then Ok true else list_mem_loop x tl
+  | List_Nil -> Ok false
   end
 
 (** [loops::list_mem]:
@@ -125,12 +125,12 @@ let rec list_nth_mut_loop_loop
   begin match ls with
   | List_Cons x tl ->
     if i = 0
-    then let back = fun ret -> Return (List_Cons ret tl) in Return (x, back)
+    then let back = fun ret -> Ok (List_Cons ret tl) in Ok (x, back)
     else
       let* i1 = u32_sub i 1 in
       let* (x1, back) = list_nth_mut_loop_loop t tl i1 in
-      let back1 = fun ret -> let* tl1 = back ret in Return (List_Cons x tl1) in
-      Return (x1, back1)
+      let back1 = fun ret -> let* tl1 = back ret in Ok (List_Cons x tl1) in
+      Ok (x1, back1)
   | List_Nil -> Fail Failure
   end
 
@@ -151,7 +151,7 @@ let rec list_nth_shared_loop_loop
   begin match ls with
   | List_Cons x tl ->
     if i = 0
-    then Return x
+    then Ok x
     else let* i1 = u32_sub i 1 in list_nth_shared_loop_loop t tl i1
   | List_Nil -> Fail Failure
   end
@@ -171,11 +171,11 @@ let rec get_elem_mut_loop
   begin match ls with
   | List_Cons y tl ->
     if y = x
-    then let back = fun ret -> Return (List_Cons ret tl) in Return (y, back)
+    then let back = fun ret -> Ok (List_Cons ret tl) in Ok (y, back)
     else
       let* (i, back) = get_elem_mut_loop x tl in
-      let back1 = fun ret -> let* tl1 = back ret in Return (List_Cons y tl1) in
-      Return (i, back1)
+      let back1 = fun ret -> let* tl1 = back ret in Ok (List_Cons y tl1) in
+      Ok (i, back1)
   | List_Nil -> Fail Failure
   end
 
@@ -190,7 +190,7 @@ let get_elem_mut
       (core_slice_index_SliceIndexUsizeSliceTInst (list_t usize)) slots 0 in
   let* (i, back) = get_elem_mut_loop x ls in
   let back1 = fun ret -> let* l = back ret in index_mut_back l in
-  Return (i, back1)
+  Ok (i, back1)
 
 (** [loops::get_elem_shared]: loop 0:
     Source: 'src/loops.rs', lines 129:0-143:1 *)
@@ -199,7 +199,7 @@ let rec get_elem_shared_loop
   Tot (result usize) (decreases (get_elem_shared_loop_decreases x ls))
   =
   begin match ls with
-  | List_Cons y tl -> if y = x then Return y else get_elem_shared_loop x tl
+  | List_Cons y tl -> if y = x then Ok y else get_elem_shared_loop x tl
   | List_Nil -> Fail Failure
   end
 
@@ -218,12 +218,12 @@ let id_mut
   (t : Type0) (ls : list_t t) :
   result ((list_t t) & (list_t t -> result (list_t t)))
   =
-  Return (ls, Return)
+  Ok (ls, Ok)
 
 (** [loops::id_shared]:
     Source: 'src/loops.rs', lines 149:0-149:45 *)
 let id_shared (t : Type0) (ls : list_t t) : result (list_t t) =
-  Return ls
+  Ok ls
 
 (** [loops::list_nth_mut_loop_with_id]: loop 0:
     Source: 'src/loops.rs', lines 154:0-165:1 *)
@@ -235,12 +235,12 @@ let rec list_nth_mut_loop_with_id_loop
   begin match ls with
   | List_Cons x tl ->
     if i = 0
-    then let back = fun ret -> Return (List_Cons ret tl) in Return (x, back)
+    then let back = fun ret -> Ok (List_Cons ret tl) in Ok (x, back)
     else
       let* i1 = u32_sub i 1 in
       let* (x1, back) = list_nth_mut_loop_with_id_loop t i1 tl in
-      let back1 = fun ret -> let* tl1 = back ret in Return (List_Cons x tl1) in
-      Return (x1, back1)
+      let back1 = fun ret -> let* tl1 = back ret in Ok (List_Cons x tl1) in
+      Ok (x1, back1)
   | List_Nil -> Fail Failure
   end
 
@@ -253,7 +253,7 @@ let list_nth_mut_loop_with_id
   let* (ls1, id_mut_back) = id_mut t ls in
   let* (x, back) = list_nth_mut_loop_with_id_loop t i ls1 in
   let back1 = fun ret -> let* l = back ret in id_mut_back l in
-  Return (x, back1)
+  Ok (x, back1)
 
 (** [loops::list_nth_shared_loop_with_id]: loop 0:
     Source: 'src/loops.rs', lines 168:0-179:1 *)
@@ -265,7 +265,7 @@ let rec list_nth_shared_loop_with_id_loop
   begin match ls with
   | List_Cons x tl ->
     if i = 0
-    then Return x
+    then Ok x
     else let* i1 = u32_sub i 1 in list_nth_shared_loop_with_id_loop t i1 tl
   | List_Nil -> Fail Failure
   end
@@ -289,17 +289,17 @@ let rec list_nth_mut_loop_pair_loop
     | List_Cons x1 tl1 ->
       if i = 0
       then
-        let back'a = fun ret -> Return (List_Cons ret tl0) in
-        let back'b = fun ret -> Return (List_Cons ret tl1) in
-        Return ((x0, x1), back'a, back'b)
+        let back'a = fun ret -> Ok (List_Cons ret tl0) in
+        let back'b = fun ret -> Ok (List_Cons ret tl1) in
+        Ok ((x0, x1), back'a, back'b)
       else
         let* i1 = u32_sub i 1 in
         let* (p, back'a, back'b) = list_nth_mut_loop_pair_loop t tl0 tl1 i1 in
         let back'a1 =
-          fun ret -> let* tl01 = back'a ret in Return (List_Cons x0 tl01) in
+          fun ret -> let* tl01 = back'a ret in Ok (List_Cons x0 tl01) in
         let back'b1 =
-          fun ret -> let* tl11 = back'b ret in Return (List_Cons x1 tl11) in
-        Return (p, back'a1, back'b1)
+          fun ret -> let* tl11 = back'b ret in Ok (List_Cons x1 tl11) in
+        Ok (p, back'a1, back'b1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
@@ -325,7 +325,7 @@ let rec list_nth_shared_loop_pair_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then Ok (x0, x1)
       else let* i1 = u32_sub i 1 in list_nth_shared_loop_pair_loop t tl0 tl1 i1
     | List_Nil -> Fail Failure
     end
@@ -353,16 +353,16 @@ let rec list_nth_mut_loop_pair_merge_loop
       then
         let back =
           fun ret ->
-            let (x, x2) = ret in Return (List_Cons x tl0, List_Cons x2 tl1) in
-        Return ((x0, x1), back)
+            let (x, x2) = ret in Ok (List_Cons x tl0, List_Cons x2 tl1) in
+        Ok ((x0, x1), back)
       else
         let* i1 = u32_sub i 1 in
         let* (p, back) = list_nth_mut_loop_pair_merge_loop t tl0 tl1 i1 in
         let back1 =
           fun ret ->
             let* (tl01, tl11) = back ret in
-            Return (List_Cons x0 tl01, List_Cons x1 tl11) in
-        Return (p, back1)
+            Ok (List_Cons x0 tl01, List_Cons x1 tl11) in
+        Ok (p, back1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
@@ -388,7 +388,7 @@ let rec list_nth_shared_loop_pair_merge_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then Ok (x0, x1)
       else
         let* i1 = u32_sub i 1 in
         list_nth_shared_loop_pair_merge_loop t tl0 tl1 i1
@@ -415,15 +415,13 @@ let rec list_nth_mut_shared_loop_pair_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then
-        let back = fun ret -> Return (List_Cons ret tl0) in
-        Return ((x0, x1), back)
+      then let back = fun ret -> Ok (List_Cons ret tl0) in Ok ((x0, x1), back)
       else
         let* i1 = u32_sub i 1 in
         let* (p, back) = list_nth_mut_shared_loop_pair_loop t tl0 tl1 i1 in
-        let back1 =
-          fun ret -> let* tl01 = back ret in Return (List_Cons x0 tl01) in
-        Return (p, back1)
+        let back1 = fun ret -> let* tl01 = back ret in Ok (List_Cons x0 tl01)
+          in
+        Ok (p, back1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
@@ -449,16 +447,14 @@ let rec list_nth_mut_shared_loop_pair_merge_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then
-        let back = fun ret -> Return (List_Cons ret tl0) in
-        Return ((x0, x1), back)
+      then let back = fun ret -> Ok (List_Cons ret tl0) in Ok ((x0, x1), back)
       else
         let* i1 = u32_sub i 1 in
         let* (p, back) = list_nth_mut_shared_loop_pair_merge_loop t tl0 tl1 i1
           in
-        let back1 =
-          fun ret -> let* tl01 = back ret in Return (List_Cons x0 tl01) in
-        Return (p, back1)
+        let back1 = fun ret -> let* tl01 = back ret in Ok (List_Cons x0 tl01)
+          in
+        Ok (p, back1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
@@ -484,15 +480,13 @@ let rec list_nth_shared_mut_loop_pair_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then
-        let back = fun ret -> Return (List_Cons ret tl1) in
-        Return ((x0, x1), back)
+      then let back = fun ret -> Ok (List_Cons ret tl1) in Ok ((x0, x1), back)
       else
         let* i1 = u32_sub i 1 in
         let* (p, back) = list_nth_shared_mut_loop_pair_loop t tl0 tl1 i1 in
-        let back1 =
-          fun ret -> let* tl11 = back ret in Return (List_Cons x1 tl11) in
-        Return (p, back1)
+        let back1 = fun ret -> let* tl11 = back ret in Ok (List_Cons x1 tl11)
+          in
+        Ok (p, back1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
@@ -518,16 +512,14 @@ let rec list_nth_shared_mut_loop_pair_merge_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then
-        let back = fun ret -> Return (List_Cons ret tl1) in
-        Return ((x0, x1), back)
+      then let back = fun ret -> Ok (List_Cons ret tl1) in Ok ((x0, x1), back)
       else
         let* i1 = u32_sub i 1 in
         let* (p, back) = list_nth_shared_mut_loop_pair_merge_loop t tl0 tl1 i1
           in
-        let back1 =
-          fun ret -> let* tl11 = back ret in Return (List_Cons x1 tl11) in
-        Return (p, back1)
+        let back1 = fun ret -> let* tl11 = back ret in Ok (List_Cons x1 tl11)
+          in
+        Ok (p, back1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
@@ -549,12 +541,12 @@ let rec ignore_input_mut_borrow_loop
   =
   if i > 0
   then let* i1 = u32_sub i 1 in ignore_input_mut_borrow_loop i1
-  else Return ()
+  else Ok ()
 
 (** [loops::ignore_input_mut_borrow]:
     Source: 'src/loops.rs', lines 345:0-345:56 *)
 let ignore_input_mut_borrow (_a : u32) (i : u32) : result u32 =
-  let* _ = ignore_input_mut_borrow_loop i in Return _a
+  let* _ = ignore_input_mut_borrow_loop i in Ok _a
 
 (** [loops::incr_ignore_input_mut_borrow]: loop 0:
     Source: 'src/loops.rs', lines 353:0-358:1 *)
@@ -564,14 +556,14 @@ let rec incr_ignore_input_mut_borrow_loop
   =
   if i > 0
   then let* i1 = u32_sub i 1 in incr_ignore_input_mut_borrow_loop i1
-  else Return ()
+  else Ok ()
 
 (** [loops::incr_ignore_input_mut_borrow]:
     Source: 'src/loops.rs', lines 353:0-353:60 *)
 let incr_ignore_input_mut_borrow (a : u32) (i : u32) : result u32 =
   let* a1 = u32_add a 1 in
   let* _ = incr_ignore_input_mut_borrow_loop i in
-  Return a1
+  Ok a1
 
 (** [loops::ignore_input_shared_borrow]: loop 0:
     Source: 'src/loops.rs', lines 362:0-366:1 *)
@@ -581,10 +573,10 @@ let rec ignore_input_shared_borrow_loop
   =
   if i > 0
   then let* i1 = u32_sub i 1 in ignore_input_shared_borrow_loop i1
-  else Return ()
+  else Ok ()
 
 (** [loops::ignore_input_shared_borrow]:
     Source: 'src/loops.rs', lines 362:0-362:59 *)
 let ignore_input_shared_borrow (_a : u32) (i : u32) : result u32 =
-  let* _ = ignore_input_shared_borrow_loop i in Return _a
+  let* _ = ignore_input_shared_borrow_loop i in Ok _a
 
diff --git a/tests/fstar/misc/NoNestedBorrows.fst b/tests/fstar/misc/NoNestedBorrows.fst
index 1a93beaa..ac443a99 100644
--- a/tests/fstar/misc/NoNestedBorrows.fst
+++ b/tests/fstar/misc/NoNestedBorrows.fst
@@ -151,20 +151,20 @@ let cast_bool_to_i32 (x : bool) : result i32 =
 (** [no_nested_borrows::cast_bool_to_bool]:
     Source: 'src/no_nested_borrows.rs', lines 137:0-137:41 *)
 let cast_bool_to_bool (x : bool) : result bool =
-  Return x
+  Ok x
 
 (** [no_nested_borrows::test2]:
     Source: 'src/no_nested_borrows.rs', lines 142:0-142:14 *)
 let test2 : result unit =
-  let* _ = u32_add 23 44 in Return ()
+  let* _ = u32_add 23 44 in Ok ()
 
 (** Unit test for [no_nested_borrows::test2] *)
-let _ = assert_norm (test2 = Return ())
+let _ = assert_norm (test2 = Ok ())
 
 (** [no_nested_borrows::get_max]:
     Source: 'src/no_nested_borrows.rs', lines 154:0-154:37 *)
 let get_max (x : u32) (y : u32) : result u32 =
-  if x >= y then Return x else Return y
+  if x >= y then Ok x else Ok y
 
 (** [no_nested_borrows::test3]:
     Source: 'src/no_nested_borrows.rs', lines 162:0-162:14 *)
@@ -172,26 +172,26 @@ let test3 : result unit =
   let* x = get_max 4 3 in
   let* y = get_max 10 11 in
   let* z = u32_add x y in
-  if not (z = 15) then Fail Failure else Return ()
+  if not (z = 15) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test3] *)
-let _ = assert_norm (test3 = Return ())
+let _ = assert_norm (test3 = Ok ())
 
 (** [no_nested_borrows::test_neg1]:
     Source: 'src/no_nested_borrows.rs', lines 169:0-169:18 *)
 let test_neg1 : result unit =
-  let* y = i32_neg 3 in if not (y = -3) then Fail Failure else Return ()
+  let* y = i32_neg 3 in if not (y = -3) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_neg1] *)
-let _ = assert_norm (test_neg1 = Return ())
+let _ = assert_norm (test_neg1 = Ok ())
 
 (** [no_nested_borrows::refs_test1]:
     Source: 'src/no_nested_borrows.rs', lines 176:0-176:19 *)
 let refs_test1 : result unit =
-  if not (1 = 1) then Fail Failure else Return ()
+  if not (1 = 1) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::refs_test1] *)
-let _ = assert_norm (refs_test1 = Return ())
+let _ = assert_norm (refs_test1 = Ok ())
 
 (** [no_nested_borrows::refs_test2]:
     Source: 'src/no_nested_borrows.rs', lines 187:0-187:19 *)
@@ -204,18 +204,18 @@ let refs_test2 : result unit =
     else
       if not (2 = 2)
       then Fail Failure
-      else if not (2 = 2) then Fail Failure else Return ()
+      else if not (2 = 2) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::refs_test2] *)
-let _ = assert_norm (refs_test2 = Return ())
+let _ = assert_norm (refs_test2 = Ok ())
 
 (** [no_nested_borrows::test_list1]:
     Source: 'src/no_nested_borrows.rs', lines 203:0-203:19 *)
 let test_list1 : result unit =
-  Return ()
+  Ok ()
 
 (** Unit test for [no_nested_borrows::test_list1] *)
-let _ = assert_norm (test_list1 = Return ())
+let _ = assert_norm (test_list1 = Ok ())
 
 (** [no_nested_borrows::test_box1]:
     Source: 'src/no_nested_borrows.rs', lines 208:0-208:18 *)
@@ -223,56 +223,53 @@ let test_box1 : result unit =
   let* (_, deref_mut_back) = alloc_boxed_Box_deref_mut i32 0 in
   let* b = deref_mut_back 1 in
   let* x = alloc_boxed_Box_deref i32 b in
-  if not (x = 1) then Fail Failure else Return ()
+  if not (x = 1) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_box1] *)
-let _ = assert_norm (test_box1 = Return ())
+let _ = assert_norm (test_box1 = Ok ())
 
 (** [no_nested_borrows::copy_int]:
     Source: 'src/no_nested_borrows.rs', lines 218:0-218:30 *)
 let copy_int (x : i32) : result i32 =
-  Return x
+  Ok x
 
 (** [no_nested_borrows::test_unreachable]:
     Source: 'src/no_nested_borrows.rs', lines 224:0-224:32 *)
 let test_unreachable (b : bool) : result unit =
-  if b then Fail Failure else Return ()
+  if b then Fail Failure else Ok ()
 
 (** [no_nested_borrows::test_panic]:
     Source: 'src/no_nested_borrows.rs', lines 232:0-232:26 *)
 let test_panic (b : bool) : result unit =
-  if b then Fail Failure else Return ()
+  if b then Fail Failure else Ok ()
 
 (** [no_nested_borrows::test_copy_int]:
     Source: 'src/no_nested_borrows.rs', lines 239:0-239:22 *)
 let test_copy_int : result unit =
-  let* y = copy_int 0 in if not (0 = y) then Fail Failure else Return ()
+  let* y = copy_int 0 in if not (0 = y) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_copy_int] *)
-let _ = assert_norm (test_copy_int = Return ())
+let _ = assert_norm (test_copy_int = Ok ())
 
 (** [no_nested_borrows::is_cons]:
     Source: 'src/no_nested_borrows.rs', lines 246:0-246:38 *)
 let is_cons (t : Type0) (l : list_t t) : result bool =
-  begin match l with
-  | List_Cons _ _ -> Return true
-  | List_Nil -> Return false
-  end
+  begin match l with | List_Cons _ _ -> Ok true | List_Nil -> Ok false end
 
 (** [no_nested_borrows::test_is_cons]:
     Source: 'src/no_nested_borrows.rs', lines 253:0-253:21 *)
 let test_is_cons : result unit =
   let* b = is_cons i32 (List_Cons 0 List_Nil) in
-  if not b then Fail Failure else Return ()
+  if not b then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_is_cons] *)
-let _ = assert_norm (test_is_cons = Return ())
+let _ = assert_norm (test_is_cons = Ok ())
 
 (** [no_nested_borrows::split_list]:
     Source: 'src/no_nested_borrows.rs', lines 259:0-259:48 *)
 let split_list (t : Type0) (l : list_t t) : result (t & (list_t t)) =
   begin match l with
-  | List_Cons hd tl -> Return (hd, tl)
+  | List_Cons hd tl -> Ok (hd, tl)
   | List_Nil -> Fail Failure
   end
 
@@ -281,18 +278,18 @@ let split_list (t : Type0) (l : list_t t) : result (t & (list_t t)) =
 let test_split_list : result unit =
   let* p = split_list i32 (List_Cons 0 List_Nil) in
   let (hd, _) = p in
-  if not (hd = 0) then Fail Failure else Return ()
+  if not (hd = 0) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_split_list] *)
-let _ = assert_norm (test_split_list = Return ())
+let _ = assert_norm (test_split_list = Ok ())
 
 (** [no_nested_borrows::choose]:
     Source: 'src/no_nested_borrows.rs', lines 274:0-274:70 *)
 let choose
   (t : Type0) (b : bool) (x : t) (y : t) : result (t & (t -> result (t & t))) =
   if b
-  then let back = fun ret -> Return (ret, y) in Return (x, back)
-  else let back = fun ret -> Return (x, ret) in Return (y, back)
+  then let back = fun ret -> Ok (ret, y) in Ok (x, back)
+  else let back = fun ret -> Ok (x, ret) in Ok (y, back)
 
 (** [no_nested_borrows::choose_test]:
     Source: 'src/no_nested_borrows.rs', lines 282:0-282:20 *)
@@ -305,15 +302,15 @@ let choose_test : result unit =
     let* (x, y) = choose_back z1 in
     if not (x = 1)
     then Fail Failure
-    else if not (y = 0) then Fail Failure else Return ()
+    else if not (y = 0) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::choose_test] *)
-let _ = assert_norm (choose_test = Return ())
+let _ = assert_norm (choose_test = Ok ())
 
 (** [no_nested_borrows::test_char]:
     Source: 'src/no_nested_borrows.rs', lines 294:0-294:26 *)
 let test_char : result char =
-  Return 'a'
+  Ok 'a'
 
 (** [no_nested_borrows::Tree]
     Source: 'src/no_nested_borrows.rs', lines 299:0-299:16 *)
@@ -332,7 +329,7 @@ and nodeElem_t (t : Type0) =
 let rec list_length (t : Type0) (l : list_t t) : result u32 =
   begin match l with
   | List_Cons _ l1 -> let* i = list_length t l1 in u32_add 1 i
-  | List_Nil -> Return 0
+  | List_Nil -> Ok 0
   end
 
 (** [no_nested_borrows::list_nth_shared]:
@@ -340,9 +337,7 @@ let rec list_length (t : Type0) (l : list_t t) : result u32 =
 let rec list_nth_shared (t : Type0) (l : list_t t) (i : u32) : result t =
   begin match l with
   | List_Cons x tl ->
-    if i = 0
-    then Return x
-    else let* i1 = u32_sub i 1 in list_nth_shared t tl i1
+    if i = 0 then Ok x else let* i1 = u32_sub i 1 in list_nth_shared t tl i1
   | List_Nil -> Fail Failure
   end
 
@@ -355,14 +350,13 @@ let rec list_nth_mut
   begin match l with
   | List_Cons x tl ->
     if i = 0
-    then let back = fun ret -> Return (List_Cons ret tl) in Return (x, back)
+    then let back = fun ret -> Ok (List_Cons ret tl) in Ok (x, back)
     else
       let* i1 = u32_sub i 1 in
       let* (x1, list_nth_mut_back) = list_nth_mut t tl i1 in
       let back =
-        fun ret -> let* tl1 = list_nth_mut_back ret in Return (List_Cons x tl1)
-        in
-      Return (x1, back)
+        fun ret -> let* tl1 = list_nth_mut_back ret in Ok (List_Cons x tl1) in
+      Ok (x1, back)
   | List_Nil -> Fail Failure
   end
 
@@ -372,7 +366,7 @@ let rec list_rev_aux
   (t : Type0) (li : list_t t) (lo : list_t t) : result (list_t t) =
   begin match li with
   | List_Cons hd tl -> list_rev_aux t tl (List_Cons hd lo)
-  | List_Nil -> Return lo
+  | List_Nil -> Ok lo
   end
 
 (** [no_nested_borrows::list_rev]:
@@ -413,10 +407,10 @@ let test_list_functions : result unit =
             then Fail Failure
             else
               let* i6 = list_nth_shared i32 ls 2 in
-              if not (i6 = 2) then Fail Failure else Return ()
+              if not (i6 = 2) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_list_functions] *)
-let _ = assert_norm (test_list_functions = Return ())
+let _ = assert_norm (test_list_functions = Ok ())
 
 (** [no_nested_borrows::id_mut_pair1]:
     Source: 'src/no_nested_borrows.rs', lines 414:0-414:89 *)
@@ -424,7 +418,7 @@ let id_mut_pair1
   (t1 t2 : Type0) (x : t1) (y : t2) :
   result ((t1 & t2) & ((t1 & t2) -> result (t1 & t2)))
   =
-  Return ((x, y), Return)
+  Ok ((x, y), Ok)
 
 (** [no_nested_borrows::id_mut_pair2]:
     Source: 'src/no_nested_borrows.rs', lines 418:0-418:88 *)
@@ -432,7 +426,7 @@ let id_mut_pair2
   (t1 t2 : Type0) (p : (t1 & t2)) :
   result ((t1 & t2) & ((t1 & t2) -> result (t1 & t2)))
   =
-  let (x, x1) = p in Return ((x, x1), Return)
+  let (x, x1) = p in Ok ((x, x1), Ok)
 
 (** [no_nested_borrows::id_mut_pair3]:
     Source: 'src/no_nested_borrows.rs', lines 422:0-422:93 *)
@@ -440,7 +434,7 @@ let id_mut_pair3
   (t1 t2 : Type0) (x : t1) (y : t2) :
   result ((t1 & t2) & (t1 -> result t1) & (t2 -> result t2))
   =
-  Return ((x, y), Return, Return)
+  Ok ((x, y), Ok, Ok)
 
 (** [no_nested_borrows::id_mut_pair4]:
     Source: 'src/no_nested_borrows.rs', lines 426:0-426:92 *)
@@ -448,7 +442,7 @@ let id_mut_pair4
   (t1 t2 : Type0) (p : (t1 & t2)) :
   result ((t1 & t2) & (t1 -> result t1) & (t2 -> result t2))
   =
-  let (x, x1) = p in Return ((x, x1), Return, Return)
+  let (x, x1) = p in Ok ((x, x1), Ok, Ok)
 
 (** [no_nested_borrows::StructWithTuple]
     Source: 'src/no_nested_borrows.rs', lines 433:0-433:34 *)
@@ -457,17 +451,17 @@ type structWithTuple_t (t1 t2 : Type0) = { p : (t1 & t2); }
 (** [no_nested_borrows::new_tuple1]:
     Source: 'src/no_nested_borrows.rs', lines 437:0-437:48 *)
 let new_tuple1 : result (structWithTuple_t u32 u32) =
-  Return { p = (1, 2) }
+  Ok { p = (1, 2) }
 
 (** [no_nested_borrows::new_tuple2]:
     Source: 'src/no_nested_borrows.rs', lines 441:0-441:48 *)
 let new_tuple2 : result (structWithTuple_t i16 i16) =
-  Return { p = (1, 2) }
+  Ok { p = (1, 2) }
 
 (** [no_nested_borrows::new_tuple3]:
     Source: 'src/no_nested_borrows.rs', lines 445:0-445:48 *)
 let new_tuple3 : result (structWithTuple_t u64 i64) =
-  Return { p = (1, 2) }
+  Ok { p = (1, 2) }
 
 (** [no_nested_borrows::StructWithPair]
     Source: 'src/no_nested_borrows.rs', lines 450:0-450:33 *)
@@ -476,7 +470,7 @@ type structWithPair_t (t1 t2 : Type0) = { p : pair_t t1 t2; }
 (** [no_nested_borrows::new_pair1]:
     Source: 'src/no_nested_borrows.rs', lines 454:0-454:46 *)
 let new_pair1 : result (structWithPair_t u32 u32) =
-  Return { p = { x = 1; y = 2 } }
+  Ok { p = { x = 1; y = 2 } }
 
 (** [no_nested_borrows::test_constants]:
     Source: 'src/no_nested_borrows.rs', lines 462:0-462:23 *)
@@ -497,44 +491,44 @@ let test_constants : result unit =
       then Fail Failure
       else
         let* swp = new_pair1 in
-        if not (swp.p.x = 1) then Fail Failure else Return ()
+        if not (swp.p.x = 1) then Fail Failure else Ok ()
 
 (** Unit test for [no_nested_borrows::test_constants] *)
-let _ = assert_norm (test_constants = Return ())
+let _ = assert_norm (test_constants = Ok ())
 
 (** [no_nested_borrows::test_weird_borrows1]:
     Source: 'src/no_nested_borrows.rs', lines 471:0-471:28 *)
 let test_weird_borrows1 : result unit =
-  Return ()
+  Ok ()
 
 (** Unit test for [no_nested_borrows::test_weird_borrows1] *)
-let _ = assert_norm (test_weird_borrows1 = Return ())
+let _ = assert_norm (test_weird_borrows1 = Ok ())
 
 (** [no_nested_borrows::test_mem_replace]:
     Source: 'src/no_nested_borrows.rs', lines 481:0-481:37 *)
 let test_mem_replace (px : u32) : result u32 =
   let (y, _) = core_mem_replace u32 px 1 in
-  if not (y = 0) then Fail Failure else Return 2
+  if not (y = 0) then Fail Failure else Ok 2
 
 (** [no_nested_borrows::test_shared_borrow_bool1]:
     Source: 'src/no_nested_borrows.rs', lines 488:0-488:47 *)
 let test_shared_borrow_bool1 (b : bool) : result u32 =
-  if b then Return 0 else Return 1
+  if b then Ok 0 else Ok 1
 
 (** [no_nested_borrows::test_shared_borrow_bool2]:
     Source: 'src/no_nested_borrows.rs', lines 501:0-501:40 *)
 let test_shared_borrow_bool2 : result u32 =
-  Return 0
+  Ok 0
 
 (** [no_nested_borrows::test_shared_borrow_enum1]:
     Source: 'src/no_nested_borrows.rs', lines 516:0-516:52 *)
 let test_shared_borrow_enum1 (l : list_t u32) : result u32 =
-  begin match l with | List_Cons _ _ -> Return 1 | List_Nil -> Return 0 end
+  begin match l with | List_Cons _ _ -> Ok 1 | List_Nil -> Ok 0 end
 
 (** [no_nested_borrows::test_shared_borrow_enum2]:
     Source: 'src/no_nested_borrows.rs', lines 528:0-528:40 *)
 let test_shared_borrow_enum2 : result u32 =
-  Return 0
+  Ok 0
 
 (** [no_nested_borrows::incr]:
     Source: 'src/no_nested_borrows.rs', lines 539:0-539:24 *)
@@ -549,7 +543,7 @@ let call_incr (x : u32) : result u32 =
 (** [no_nested_borrows::read_then_incr]:
     Source: 'src/no_nested_borrows.rs', lines 548:0-548:41 *)
 let read_then_incr (x : u32) : result (u32 & u32) =
-  let* x1 = u32_add x 1 in Return (x, x1)
+  let* x1 = u32_add x 1 in Ok (x, x1)
 
 (** [no_nested_borrows::Tuple]
     Source: 'src/no_nested_borrows.rs', lines 554:0-554:24 *)
@@ -558,12 +552,12 @@ type tuple_t (t1 t2 : Type0) = t1 * t2
 (** [no_nested_borrows::use_tuple_struct]:
     Source: 'src/no_nested_borrows.rs', lines 556:0-556:48 *)
 let use_tuple_struct (x : tuple_t u32 u32) : result (tuple_t u32 u32) =
-  let (_, i) = x in Return (1, i)
+  let (_, i) = x in Ok (1, i)
 
 (** [no_nested_borrows::create_tuple_struct]:
     Source: 'src/no_nested_borrows.rs', lines 560:0-560:61 *)
 let create_tuple_struct (x : u32) (y : u64) : result (tuple_t u32 u64) =
-  Return (x, y)
+  Ok (x, y)
 
 (** [no_nested_borrows::IdType]
     Source: 'src/no_nested_borrows.rs', lines 565:0-565:20 *)
@@ -572,10 +566,10 @@ type idType_t (t : Type0) = t
 (** [no_nested_borrows::use_id_type]:
     Source: 'src/no_nested_borrows.rs', lines 567:0-567:40 *)
 let use_id_type (t : Type0) (x : idType_t t) : result t =
-  Return x
+  Ok x
 
 (** [no_nested_borrows::create_id_type]:
     Source: 'src/no_nested_borrows.rs', lines 571:0-571:43 *)
 let create_id_type (t : Type0) (x : t) : result (idType_t t) =
-  Return x
+  Ok x
 
diff --git a/tests/fstar/misc/Paper.fst b/tests/fstar/misc/Paper.fst
index c2f47ad1..e6b4eb25 100644
--- a/tests/fstar/misc/Paper.fst
+++ b/tests/fstar/misc/Paper.fst
@@ -13,18 +13,18 @@ let ref_incr (x : i32) : result i32 =
 (** [paper::test_incr]:
     Source: 'src/paper.rs', lines 8:0-8:18 *)
 let test_incr : result unit =
-  let* x = ref_incr 0 in if not (x = 1) then Fail Failure else Return ()
+  let* x = ref_incr 0 in if not (x = 1) then Fail Failure else Ok ()
 
 (** Unit test for [paper::test_incr] *)
-let _ = assert_norm (test_incr = Return ())
+let _ = assert_norm (test_incr = Ok ())
 
 (** [paper::choose]:
     Source: 'src/paper.rs', lines 15:0-15:70 *)
 let choose
   (t : Type0) (b : bool) (x : t) (y : t) : result (t & (t -> result (t & t))) =
   if b
-  then let back = fun ret -> Return (ret, y) in Return (x, back)
-  else let back = fun ret -> Return (x, ret) in Return (y, back)
+  then let back = fun ret -> Ok (ret, y) in Ok (x, back)
+  else let back = fun ret -> Ok (x, ret) in Ok (y, back)
 
 (** [paper::test_choose]:
     Source: 'src/paper.rs', lines 23:0-23:20 *)
@@ -37,10 +37,10 @@ let test_choose : result unit =
     let* (x, y) = choose_back z1 in
     if not (x = 1)
     then Fail Failure
-    else if not (y = 0) then Fail Failure else Return ()
+    else if not (y = 0) then Fail Failure else Ok ()
 
 (** Unit test for [paper::test_choose] *)
-let _ = assert_norm (test_choose = Return ())
+let _ = assert_norm (test_choose = Ok ())
 
 (** [paper::List]
     Source: 'src/paper.rs', lines 35:0-35:16 *)
@@ -57,14 +57,13 @@ let rec list_nth_mut
   begin match l with
   | List_Cons x tl ->
     if i = 0
-    then let back = fun ret -> Return (List_Cons ret tl) in Return (x, back)
+    then let back = fun ret -> Ok (List_Cons ret tl) in Ok (x, back)
     else
       let* i1 = u32_sub i 1 in
       let* (x1, list_nth_mut_back) = list_nth_mut t tl i1 in
       let back =
-        fun ret -> let* tl1 = list_nth_mut_back ret in Return (List_Cons x tl1)
-        in
-      Return (x1, back)
+        fun ret -> let* tl1 = list_nth_mut_back ret in Ok (List_Cons x tl1) in
+      Ok (x1, back)
   | List_Nil -> Fail Failure
   end
 
@@ -73,7 +72,7 @@ let rec list_nth_mut
 let rec sum (l : list_t i32) : result i32 =
   begin match l with
   | List_Cons x tl -> let* i = sum tl in i32_add x i
-  | List_Nil -> Return 0
+  | List_Nil -> Ok 0
   end
 
 (** [paper::test_nth]:
@@ -85,10 +84,10 @@ let test_nth : result unit =
   let* x1 = i32_add x 1 in
   let* l2 = list_nth_mut_back x1 in
   let* i = sum l2 in
-  if not (i = 7) then Fail Failure else Return ()
+  if not (i = 7) then Fail Failure else Ok ()
 
 (** Unit test for [paper::test_nth] *)
-let _ = assert_norm (test_nth = Return ())
+let _ = assert_norm (test_nth = Ok ())
 
 (** [paper::call_choose]:
     Source: 'src/paper.rs', lines 76:0-76:44 *)
@@ -97,5 +96,5 @@ let call_choose (p : (u32 & u32)) : result u32 =
   let* (pz, choose_back) = choose u32 true px py in
   let* pz1 = u32_add pz 1 in
   let* (px1, _) = choose_back pz1 in
-  Return px1
+  Ok px1
 
diff --git a/tests/fstar/misc/PoloniusList.fst b/tests/fstar/misc/PoloniusList.fst
index 4203247e..c0bc592e 100644
--- a/tests/fstar/misc/PoloniusList.fst
+++ b/tests/fstar/misc/PoloniusList.fst
@@ -20,13 +20,13 @@ let rec get_list_at_x
   begin match ls with
   | List_Cons hd tl ->
     if hd = x
-    then Return (List_Cons hd tl, Return)
+    then Ok (List_Cons hd tl, Ok)
     else
       let* (l, get_list_at_x_back) = get_list_at_x tl x in
       let back =
-        fun ret ->
-          let* tl1 = get_list_at_x_back ret in Return (List_Cons hd tl1) in
-      Return (l, back)
-  | List_Nil -> Return (List_Nil, Return)
+        fun ret -> let* tl1 = get_list_at_x_back ret in Ok (List_Cons hd tl1)
+        in
+      Ok (l, back)
+  | List_Nil -> Ok (List_Nil, Ok)
   end
 
diff --git a/tests/fstar/misc/Primitives.fst b/tests/fstar/misc/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/misc/Primitives.fst
+++ b/tests/fstar/misc/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/traits/Primitives.fst b/tests/fstar/traits/Primitives.fst
index fca80829..acdb09dc 100644
--- a/tests/fstar/traits/Primitives.fst
+++ b/tests/fstar/traits/Primitives.fst
@@ -23,11 +23,11 @@ type error : Type0 =
 | OutOfFuel
 
 type result (a : Type0) : Type0 =
-| Return : v:a -> result a
+| Ok : v:a -> result a
 | Fail : e:error -> result a
 
 // Monadic return operator
-unfold let return (#a : Type0) (x : a) : result a = Return x
+unfold let return (#a : Type0) (x : a) : result a = Ok x
 
 // Monadic bind operator.
 // Allows to use the notation:
@@ -36,17 +36,17 @@ unfold let return (#a : Type0) (x : a) : result a = Return x
 // ...
 // ```
 unfold let (let*) (#a #b : Type0) (m: result a)
-  (f: (x:a) -> Pure (result b) (requires (m == Return x)) (ensures fun _ -> True)) :
+  (f: (x:a) -> Pure (result b) (requires (m == Ok x)) (ensures fun _ -> True)) :
   result b =
   match m with
-  | Return x -> f x
+  | Ok x -> f x
   | Fail e   -> Fail e
 
 // Monadic assert(...)
-let massert (b:bool) : result unit = if b then Return () else Fail Failure
+let massert (b:bool) : result unit = if b then Ok () else Fail Failure
 
 // Normalize and unwrap a successful result (used for globals).
-let eval_global (#a : Type0) (x : result a{Return? (normalize_term x)}) : a = Return?.v x
+let eval_global (#a : Type0) (x : result a{Ok? (normalize_term x)}) : a = Ok?.v x
 
 (*** Misc *)
 type char = FStar.Char.char
@@ -144,7 +144,7 @@ let scalar_max (ty : scalar_ty) : int =
 type scalar (ty : scalar_ty) : eqtype = x:int{scalar_min ty <= x && x <= scalar_max ty}
 
 let mk_scalar (ty : scalar_ty) (x : int) : result (scalar ty) =
-  if scalar_min ty <= x && scalar_max ty >= x then Return x else Fail Failure
+  if scalar_min ty <= x && scalar_max ty >= x then Ok x else Fail Failure
 
 let scalar_neg (#ty : scalar_ty) (x : scalar ty) : result (scalar ty) = mk_scalar ty (-x)
 
@@ -498,9 +498,9 @@ type core_ops_range_Range (a : Type0) = {
 
 (*** [alloc] *)
 
-let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Return x
+let alloc_boxed_Box_deref (t : Type0) (x : t) : result t = Ok x
 let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
-  Return (x, (fun x -> Return x))
+  Ok (x, (fun x -> Ok x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -528,20 +528,20 @@ let mk_array (a : Type0) (n : usize)
   l
 
 let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let array_update_usize (a : Type0) (n : usize) (x : array a n) (i : usize) (nx : a) :
   result (array a n) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let array_index_mut_usize (a : Type0) (n : usize) (x : array a n) (i : usize) :
   result (a & (a -> result (array a n))) =
   match array_index_usize a n x i with
   | Fail e -> Fail e
-  | Return v ->
-    Return (v, array_update_usize a n x i)
+  | Ok v ->
+    Ok (v, array_update_usize a n x i)
 
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
@@ -549,30 +549,30 @@ type slice (a : Type0) = s:list a{length s <= usize_max}
 let slice_len (a : Type0) (s : slice a) : usize = length s
 
 let slice_index_usize (a : Type0) (x : slice a) (i : usize) : result a =
-  if i < length x then Return (index x i)
+  if i < length x then Ok (index x i)
   else Fail Failure
 
 let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (slice a) =
-  if i < length x then Return (list_update x i nx)
+  if i < length x then Ok (list_update x i nx)
   else Fail Failure
 
 let slice_index_mut_usize (a : Type0) (s : slice a) (i : usize) :
   result (a & (a -> result (slice a))) =
   match slice_index_usize a s i with
   | Fail e -> Fail e
-  | Return x ->
-    Return (x, slice_update_usize a s i)
+  | Ok x ->
+    Ok (x, slice_update_usize a s i)
 
 (*** Subslices *)
 
-let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
+let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Ok x
 let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : result (array a n) =
-  if length s = n then Return s
+  if length s = n then Ok s
   else Fail Failure
 
 let array_to_slice_mut (a : Type0) (n : usize) (x : array a n) :
   result (slice a & (slice a -> result (array a n))) =
-  Return (x, array_from_slice a n x)
+  Ok (x, array_from_slice a n x)
 
 // TODO: finish the definitions below (there lacks [List.drop] and [List.take] in the standard library *)
 let array_subslice (a : Type0) (n : usize) (x : array a n) (r : core_ops_range_Range usize) : result (slice a) =
@@ -598,16 +598,16 @@ let alloc_vec_Vec_len (a : Type0) (v : alloc_vec_Vec a) : usize = length v
 
 // Helper
 let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : result a =
-  if i < length v then Return (index v i) else Fail Failure
+  if i < length v then Ok (index v i) else Fail Failure
 // Helper
 let alloc_vec_Vec_update_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 let alloc_vec_Vec_index_mut_usize (#a : Type0) (v: alloc_vec_Vec a) (i: usize) :
   result (a & (a → result (alloc_vec_Vec a))) =
   match alloc_vec_Vec_index_usize v i with
-  | Return x ->
-    Return (x, alloc_vec_Vec_update_usize v i)
+  | Ok x ->
+    Ok (x, alloc_vec_Vec_update_usize v i)
   | Fail e -> Fail e
 
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
@@ -616,17 +616,17 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   (ensures (fun res ->
     match res with
     | Fail e -> e == Failure
-    | Return v' -> length v' = length v + 1)) =
+    | Ok v' -> length v' = length v + 1)) =
   if length v < usize_max then begin
     (**) assert_norm(length [x] == 1);
     (**) append_length v [x];
     (**) assert(length (append v [x]) = length v + 1);
-    Return (append v [x])
+    Ok (append v [x])
     end
   else Fail Failure
 
 let alloc_vec_Vec_insert (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result (alloc_vec_Vec a) =
-  if i < length v then Return (list_update v i x) else Fail Failure
+  if i < length v then Ok (list_update v i x) else Fail Failure
 
 // Trait declaration: [core::slice::index::private_slice_index::Sealed]
 type core_slice_index_private_slice_index_Sealed (self : Type0) = unit
@@ -650,7 +650,7 @@ let core_slice_index_Slice_index
   let* x = inst.get i s in
   match x with
   | None -> Fail Failure
-  | Some x -> Return x
+  | Some x -> Ok x
 
 // [core::slice::index::Range:::get]: forward function
 let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize) (s : slice t) :
diff --git a/tests/fstar/traits/Traits.fst b/tests/fstar/traits/Traits.fst
index 199d49bf..1f0293a0 100644
--- a/tests/fstar/traits/Traits.fst
+++ b/tests/fstar/traits/Traits.fst
@@ -12,7 +12,7 @@ noeq type boolTrait_t (self : Type0) = { get_bool : self -> result bool; }
 (** [traits::{(traits::BoolTrait for bool)}::get_bool]:
     Source: 'src/traits.rs', lines 12:4-12:30 *)
 let boolTraitBool_get_bool (self : bool) : result bool =
-  Return self
+  Ok self
 
 (** Trait implementation: [traits::{(traits::BoolTrait for bool)}]
     Source: 'src/traits.rs', lines 11:0-11:23 *)
@@ -24,18 +24,18 @@ let boolTrait_ret_true
   (#self : Type0) (self_clause : boolTrait_t self) (self1 : self) :
   result bool
   =
-  Return true
+  Ok true
 
 (** [traits::test_bool_trait_bool]:
     Source: 'src/traits.rs', lines 17:0-17:44 *)
 let test_bool_trait_bool (x : bool) : result bool =
   let* b = boolTraitBool_get_bool x in
-  if b then boolTrait_ret_true boolTraitBool x else Return false
+  if b then boolTrait_ret_true boolTraitBool x else Ok false
 
 (** [traits::{(traits::BoolTrait for core::option::Option<T>)#1}::get_bool]:
     Source: 'src/traits.rs', lines 23:4-23:30 *)
 let boolTraitOption_get_bool (t : Type0) (self : option t) : result bool =
-  begin match self with | None -> Return false | Some _ -> Return true end
+  begin match self with | None -> Ok false | Some _ -> Ok true end
 
 (** Trait implementation: [traits::{(traits::BoolTrait for core::option::Option<T>)#1}]
     Source: 'src/traits.rs', lines 22:0-22:31 *)
@@ -47,7 +47,7 @@ let boolTraitOption (t : Type0) : boolTrait_t (option t) = {
     Source: 'src/traits.rs', lines 31:0-31:54 *)
 let test_bool_trait_option (t : Type0) (x : option t) : result bool =
   let* b = boolTraitOption_get_bool t x in
-  if b then boolTrait_ret_true (boolTraitOption t) x else Return false
+  if b then boolTrait_ret_true (boolTraitOption t) x else Ok false
 
 (** [traits::test_bool_trait]:
     Source: 'src/traits.rs', lines 35:0-35:50 *)
@@ -62,7 +62,7 @@ noeq type toU64_t (self : Type0) = { to_u64 : self -> result u64; }
 (** [traits::{(traits::ToU64 for u64)#2}::to_u64]:
     Source: 'src/traits.rs', lines 44:4-44:26 *)
 let toU64U64_to_u64 (self : u64) : result u64 =
-  Return self
+  Ok self
 
 (** Trait implementation: [traits::{(traits::ToU64 for u64)#2}]
     Source: 'src/traits.rs', lines 43:0-43:18 *)
@@ -133,7 +133,7 @@ noeq type toType_t (self t : Type0) = { to_type : self -> result t; }
 (** [traits::{(traits::ToType<bool> for u64)#5}::to_type]:
     Source: 'src/traits.rs', lines 93:4-93:28 *)
 let toTypeU64Bool_to_type (self : u64) : result bool =
-  Return (self > 0)
+  Ok (self > 0)
 
 (** Trait implementation: [traits::{(traits::ToType<bool> for u64)#5}]
     Source: 'src/traits.rs', lines 92:0-92:25 *)
@@ -188,7 +188,7 @@ noeq type testType_test_TestTrait_t (self : Type0) = {
     Source: 'src/traits.rs', lines 139:12-139:34 *)
 let testType_test_TestTraittraitsTestTypetestTestType1_test
   (self : testType_test_TestType1_t) : result bool =
-  Return (self > 1)
+  Ok (self > 1)
 
 (** Trait implementation: [traits::{traits::TestType<T>#6}::test::{(traits::{traits::TestType<T>#6}::test::TestTrait for traits::{traits::TestType<T>#6}::test::TestType1)}]
     Source: 'src/traits.rs', lines 138:8-138:36 *)
@@ -206,7 +206,7 @@ let testType_test
   let* x1 = toU64Inst.to_u64 x in
   if x1 > 0
   then testType_test_TestTraittraitsTestTypetestTestType1_test 0
-  else Return false
+  else Ok false
 
 (** [traits::BoolWrapper]
     Source: 'src/traits.rs', lines 150:0-150:22 *)
@@ -231,7 +231,7 @@ let toTypetraitsBoolWrapperT (t : Type0) (toTypeBoolTInst : toType_t bool t) :
     Source: 'src/traits.rs', lines 164:4-164:21 *)
 let with_const_ty_len2_default_body (self : Type0) (len : usize)
   : result usize =
-  Return 32
+  Ok 32
 let with_const_ty_len2_default (self : Type0) (len : usize) : usize =
   eval_global (with_const_ty_len2_default_body self len)
 
@@ -248,14 +248,14 @@ noeq type withConstTy_t (self : Type0) (len : usize) = {
 
 (** [traits::{(traits::WithConstTy<32: usize> for bool)#8}::LEN1]
     Source: 'src/traits.rs', lines 175:4-175:21 *)
-let with_const_ty_bool32_len1_body : result usize = Return 12
+let with_const_ty_bool32_len1_body : result usize = Ok 12
 let with_const_ty_bool32_len1 : usize =
   eval_global with_const_ty_bool32_len1_body
 
 (** [traits::{(traits::WithConstTy<32: usize> for bool)#8}::f]:
     Source: 'src/traits.rs', lines 180:4-180:39 *)
 let withConstTyBool32_f (i : u64) (a : array u8 32) : result u64 =
-  Return i
+  Ok i
 
 (** Trait implementation: [traits::{(traits::WithConstTy<32: usize> for bool)#8}]
     Source: 'src/traits.rs', lines 174:0-174:29 *)
@@ -274,7 +274,7 @@ let use_with_const_ty1
   (h : Type0) (len : usize) (withConstTyInst : withConstTy_t h len) :
   result usize
   =
-  Return withConstTyInst.cLEN1
+  Ok withConstTyInst.cLEN1
 
 (** [traits::use_with_const_ty2]:
     Source: 'src/traits.rs', lines 187:0-187:73 *)
@@ -283,7 +283,7 @@ let use_with_const_ty2
   (w : withConstTyInst.tW) :
   result unit
   =
-  Return ()
+  Ok ()
 
 (** [traits::use_with_const_ty3]:
     Source: 'src/traits.rs', lines 189:0-189:80 *)
@@ -297,7 +297,7 @@ let use_with_const_ty3
 (** [traits::test_where1]:
     Source: 'src/traits.rs', lines 193:0-193:40 *)
 let test_where1 (t : Type0) (_x : t) : result unit =
-  Return ()
+  Ok ()
 
 (** [traits::test_where2]:
     Source: 'src/traits.rs', lines 194:0-194:57 *)
@@ -305,7 +305,7 @@ let test_where2
   (t : Type0) (withConstTyT32Inst : withConstTy_t t 32) (_x : u32) :
   result unit
   =
-  Return ()
+  Ok ()
 
 (** Trait declaration: [traits::ParentTrait0]
     Source: 'src/traits.rs', lines 200:0-200:22 *)
@@ -347,7 +347,7 @@ let order1
   parentTrait0_t u) :
   result unit
   =
-  Return ()
+  Ok ()
 
 (** Trait declaration: [traits::ChildTrait1]
     Source: 'src/traits.rs', lines 222:0-222:35 *)
@@ -421,7 +421,7 @@ let parentTrait2U32 : parentTrait2_t u32 = {
 (** [traits::{(traits::ChildTrait2 for u32)#13}::convert]:
     Source: 'src/traits.rs', lines 273:4-273:29 *)
 let childTrait2U32_convert (x : u32) : result u32 =
-  Return x
+  Ok x
 
 (** Trait implementation: [traits::{(traits::ChildTrait2 for u32)#13}]
     Source: 'src/traits.rs', lines 272:0-272:24 *)
@@ -468,7 +468,7 @@ noeq type trait_t (self : Type0) = { cLEN : usize; }
 
 (** [traits::{(traits::Trait for @Array<T, N>)#14}::LEN]
     Source: 'src/traits.rs', lines 315:4-315:20 *)
-let trait_array_len_body (t : Type0) (n : usize) : result usize = Return n
+let trait_array_len_body (t : Type0) (n : usize) : result usize = Ok n
 let trait_array_len (t : Type0) (n : usize) : usize =
   eval_global (trait_array_len_body t n)
 
@@ -482,7 +482,7 @@ let traitArray (t : Type0) (n : usize) : trait_t (array t n) = {
     Source: 'src/traits.rs', lines 319:4-319:20 *)
 let traittraits_wrapper_len_body (t : Type0) (traitInst : trait_t t)
   : result usize =
-  Return 0
+  Ok 0
 let traittraits_wrapper_len (t : Type0) (traitInst : trait_t t) : usize =
   eval_global (traittraits_wrapper_len_body t traitInst)
 
@@ -496,7 +496,7 @@ let traittraitsWrapper (t : Type0) (traitInst : trait_t t) : trait_t (wrapper_t
 (** [traits::use_wrapper_len]:
     Source: 'src/traits.rs', lines 322:0-322:43 *)
 let use_wrapper_len (t : Type0) (traitInst : trait_t t) : result usize =
-  Return (traittraitsWrapper t traitInst).cLEN
+  Ok (traittraitsWrapper t traitInst).cLEN
 
 (** [traits::Foo]
     Source: 'src/traits.rs', lines 326:0-326:20 *)
@@ -513,7 +513,7 @@ type core_result_Result_t (t e : Type0) =
     Source: 'src/traits.rs', lines 332:4-332:33 *)
 let foo_foo_body (t u : Type0) (traitInst : trait_t t)
   : result (core_result_Result_t t i32) =
-  Return (Core_result_Result_Err 0)
+  Ok (Core_result_Result_Err 0)
 let foo_foo (t u : Type0) (traitInst : trait_t t)
   : core_result_Result_t t i32 =
   eval_global (foo_foo_body t u traitInst)
@@ -522,11 +522,11 @@ let foo_foo (t u : Type0) (traitInst : trait_t t)
     Source: 'src/traits.rs', lines 335:0-335:48 *)
 let use_foo1
   (t u : Type0) (traitInst : trait_t t) : result (core_result_Result_t t i32) =
-  Return (foo_foo t u traitInst)
+  Ok (foo_foo t u traitInst)
 
 (** [traits::use_foo2]:
     Source: 'src/traits.rs', lines 339:0-339:48 *)
 let use_foo2
   (t u : Type0) (traitInst : trait_t u) : result (core_result_Result_t u i32) =
-  Return (foo_foo u t traitInst)
+  Ok (foo_foo u t traitInst)