Merge pull request #64 from AeneasVerif/son/merge_back

Merge the forward/backward functions

9 files changed, 518 insertions, 823 deletions

diff --git a/tests/fstar/misc/Bitwise.fst b/tests/fstar/misc/Bitwise.fst
index d7ba2c57..7330f07a 100644
--- a/tests/fstar/misc/Bitwise.fst
+++ b/tests/fstar/misc/Bitwise.fst
@@ -5,27 +5,27 @@ open Primitives
 
 #set-options "--z3rlimit 50 --fuel 1 --ifuel 1"
 
-(** [bitwise::shift_u32]: forward function
+(** [bitwise::shift_u32]:
     Source: 'src/bitwise.rs', lines 3:0-3:31 *)
 let shift_u32 (a : u32) : result u32 =
   let* t = u32_shr #Usize a 16 in u32_shl #Usize t 16
 
-(** [bitwise::shift_i32]: forward function
+(** [bitwise::shift_i32]:
     Source: 'src/bitwise.rs', lines 10:0-10:31 *)
 let shift_i32 (a : i32) : result i32 =
   let* t = i32_shr #Isize a 16 in i32_shl #Isize t 16
 
-(** [bitwise::xor_u32]: forward function
+(** [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)
 
-(** [bitwise::or_u32]: forward function
+(** [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)
 
-(** [bitwise::and_u32]: forward function
+(** [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)
diff --git a/tests/fstar/misc/Constants.fst b/tests/fstar/misc/Constants.fst
index daeefbb0..7bf42b46 100644
--- a/tests/fstar/misc/Constants.fst
+++ b/tests/fstar/misc/Constants.fst
@@ -20,7 +20,7 @@ let x1_c : u32 = eval_global x1_body
 let x2_body : result u32 = Return 3
 let x2_c : u32 = eval_global x2_body
 
-(** [constants::incr]: forward function
+(** [constants::incr]:
     Source: 'src/constants.rs', lines 17:0-17:32 *)
 let incr (n : u32) : result u32 =
   u32_add n 1
@@ -30,7 +30,7 @@ let incr (n : u32) : result u32 =
 let x3_body : result u32 = incr 32
 let x3_c : u32 = eval_global x3_body
 
-(** [constants::mk_pair0]: forward function
+(** [constants::mk_pair0]:
     Source: 'src/constants.rs', lines 23:0-23:51 *)
 let mk_pair0 (x : u32) (y : u32) : result (u32 & u32) =
   Return (x, y)
@@ -39,7 +39,7 @@ let mk_pair0 (x : u32) (y : u32) : result (u32 & u32) =
     Source: 'src/constants.rs', lines 36:0-36:23 *)
 type pair_t (t1 t2 : Type0) = { x : t1; y : t2; }
 
-(** [constants::mk_pair1]: forward function
+(** [constants::mk_pair1]:
     Source: 'src/constants.rs', lines 27:0-27:55 *)
 let mk_pair1 (x : u32) (y : u32) : result (pair_t u32 u32) =
   Return { x = x; y = y }
@@ -68,7 +68,7 @@ let p3_c : pair_t u32 u32 = eval_global p3_body
     Source: 'src/constants.rs', lines 49:0-49:18 *)
 type wrap_t (t : Type0) = { value : t; }
 
-(** [constants::{constants::Wrap<T>}::new]: forward function
+(** [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 }
@@ -78,7 +78,7 @@ let wrap_new (t : Type0) (value : t) : result (wrap_t t) =
 let y_body : result (wrap_t i32) = wrap_new i32 2
 let y_c : wrap_t i32 = eval_global y_body
 
-(** [constants::unwrap_y]: forward function
+(** [constants::unwrap_y]:
     Source: 'src/constants.rs', lines 43:0-43:30 *)
 let unwrap_y : result i32 =
   Return y_c.value
@@ -93,12 +93,12 @@ let yval_c : i32 = eval_global yval_body
 let get_z1_z1_body : result i32 = Return 3
 let get_z1_z1_c : i32 = eval_global get_z1_z1_body
 
-(** [constants::get_z1]: forward function
+(** [constants::get_z1]:
     Source: 'src/constants.rs', lines 61:0-61:28 *)
 let get_z1 : result i32 =
   Return get_z1_z1_c
 
-(** [constants::add]: forward function
+(** [constants::add]:
     Source: 'src/constants.rs', lines 66:0-66:39 *)
 let add (a : i32) (b : i32) : result i32 =
   i32_add a b
@@ -118,10 +118,10 @@ let q2_c : i32 = eval_global q2_body
 let q3_body : result i32 = add q2_c 3
 let q3_c : i32 = eval_global q3_body
 
-(** [constants::get_z2]: forward function
+(** [constants::get_z2]:
     Source: 'src/constants.rs', lines 70:0-70:28 *)
 let get_z2 : result i32 =
-  let* i = get_z1 in let* i0 = add i q3_c in add q1_c i0
+  let* i = get_z1 in let* i1 = add i q3_c in add q1_c i1
 
 (** [constants::S1]
     Source: 'src/constants.rs', lines 80:0-80:18 *)
diff --git a/tests/fstar/misc/External.Funs.fst b/tests/fstar/misc/External.Funs.fst
index 00995634..6672b523 100644
--- a/tests/fstar/misc/External.Funs.fst
+++ b/tests/fstar/misc/External.Funs.fst
@@ -7,78 +7,48 @@ include External.FunsExternal
 
 #set-options "--z3rlimit 50 --fuel 1 --ifuel 1"
 
-(** [external::swap]: forward function
+(** [external::swap]:
     Source: 'src/external.rs', lines 6:0-6:46 *)
-let swap (t : Type0) (x : t) (y : t) (st : state) : result (state & unit) =
-  let* (st0, _) = core_mem_swap t x y st in
-  let* (st1, _) = core_mem_swap_back0 t x y st st0 in
-  let* (st2, _) = core_mem_swap_back1 t x y st st1 in
-  Return (st2, ())
+let swap (t : Type0) (x : t) (y : t) (st : state) : result (state & (t & t)) =
+  core_mem_swap t x y st
 
-(** [external::swap]: backward function 0
-    Source: 'src/external.rs', lines 6:0-6:46 *)
-let swap_back
-  (t : Type0) (x : t) (y : t) (st : state) (st0 : state) :
-  result (state & (t & t))
-  =
-  let* (st1, _) = core_mem_swap t x y st in
-  let* (st2, x0) = core_mem_swap_back0 t x y st st1 in
-  let* (_, y0) = core_mem_swap_back1 t x y st st2 in
-  Return (st0, (x0, y0))
-
-(** [external::test_new_non_zero_u32]: forward function
+(** [external::test_new_non_zero_u32]:
     Source: 'src/external.rs', lines 11:0-11:60 *)
 let test_new_non_zero_u32
   (x : u32) (st : state) : result (state & core_num_nonzero_NonZeroU32_t) =
-  let* (st0, o) = core_num_nonzero_NonZeroU32_new x st in
-  core_option_Option_unwrap core_num_nonzero_NonZeroU32_t o st0
+  let* (st1, o) = core_num_nonzero_NonZeroU32_new x st in
+  core_option_Option_unwrap core_num_nonzero_NonZeroU32_t o st1
 
-(** [external::test_vec]: forward function
+(** [external::test_vec]:
     Source: 'src/external.rs', lines 17:0-17:17 *)
 let test_vec : result unit =
-  let v = alloc_vec_Vec_new u32 in
-  let* _ = alloc_vec_Vec_push u32 v 0 in
-  Return ()
+  let* _ = alloc_vec_Vec_push u32 (alloc_vec_Vec_new u32) 0 in Return ()
 
 (** Unit test for [external::test_vec] *)
 let _ = assert_norm (test_vec = Return ())
 
-(** [external::custom_swap]: forward function
-    Source: 'src/external.rs', lines 24:0-24:66 *)
-let custom_swap (t : Type0) (x : t) (y : t) (st : state) : result (state & t) =
-  let* (st0, _) = core_mem_swap t x y st in
-  let* (st1, x0) = core_mem_swap_back0 t x y st st0 in
-  let* (st2, _) = core_mem_swap_back1 t x y st st1 in
-  Return (st2, x0)
-
-(** [external::custom_swap]: backward function 0
+(** [external::custom_swap]:
     Source: 'src/external.rs', lines 24:0-24:66 *)
-let custom_swap_back
-  (t : Type0) (x : t) (y : t) (st : state) (ret : t) (st0 : state) :
-  result (state & (t & t))
+let custom_swap
+  (t : Type0) (x : t) (y : t) (st : state) :
+  result (state & (t & (t -> state -> result (state & (t & t)))))
   =
-  let* (st1, _) = core_mem_swap t x y st in
-  let* (st2, _) = core_mem_swap_back0 t x y st st1 in
-  let* (_, y0) = core_mem_swap_back1 t x y st st2 in
-  Return (st0, (ret, y0))
-
-(** [external::test_custom_swap]: forward function
-    Source: 'src/external.rs', lines 29:0-29:59 *)
-let test_custom_swap (x : u32) (y : u32) (st : state) : result (state & unit) =
-  let* (st0, _) = custom_swap u32 x y st in Return (st0, ())
+  let* (st1, (x1, x2)) = core_mem_swap t x y st in
+  let back_'a = fun ret st2 -> Return (st2, (ret, x2)) in
+  Return (st1, (x1, back_'a))
 
-(** [external::test_custom_swap]: backward function 0
+(** [external::test_custom_swap]:
     Source: 'src/external.rs', lines 29:0-29:59 *)
-let test_custom_swap_back
-  (x : u32) (y : u32) (st : state) (st0 : state) :
-  result (state & (u32 & u32))
-  =
-  custom_swap_back u32 x y st 1 st0
+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))
 
-(** [external::test_swap_non_zero]: forward function
+(** [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* (st0, _) = swap u32 x 0 st in
-  let* (st1, (x0, _)) = swap_back u32 x 0 st st0 in
-  if x0 = 0 then Fail Failure else Return (st1, x0)
+  let* (st1, p) = swap u32 x 0 st in
+  let (x1, _) = p in
+  if x1 = 0 then Fail Failure else Return (st1, x1)
 
diff --git a/tests/fstar/misc/External.FunsExternal.fsti b/tests/fstar/misc/External.FunsExternal.fsti
index 923a1101..a412aea9 100644
--- a/tests/fstar/misc/External.FunsExternal.fsti
+++ b/tests/fstar/misc/External.FunsExternal.fsti
@@ -6,26 +6,16 @@ include External.Types
 
 #set-options "--z3rlimit 50 --fuel 1 --ifuel 1"
 
-(** [core::mem::swap]: forward function
+(** [core::mem::swap]:
     Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/mem/mod.rs', lines 726:0-726:42 *)
-val core_mem_swap (t : Type0) : t -> t -> state -> result (state & unit)
+val core_mem_swap (t : Type0) : t -> t -> state -> result (state & (t & t))
 
-(** [core::mem::swap]: backward function 0
-    Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/mem/mod.rs', lines 726:0-726:42 *)
-val core_mem_swap_back0
-  (t : Type0) : t -> t -> state -> state -> result (state & t)
-
-(** [core::mem::swap]: backward function 1
-    Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/mem/mod.rs', lines 726:0-726:42 *)
-val core_mem_swap_back1
-  (t : Type0) : t -> t -> state -> state -> result (state & t)
-
-(** [core::num::nonzero::{core::num::nonzero::NonZeroU32#14}::new]: forward function
+(** [core::num::nonzero::{core::num::nonzero::NonZeroU32#14}::new]:
     Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/num/nonzero.rs', lines 79:16-79:57 *)
 val core_num_nonzero_NonZeroU32_new
   : u32 -> state -> result (state & (option core_num_nonzero_NonZeroU32_t))
 
-(** [core::option::{core::option::Option<T>}::unwrap]: forward function
+(** [core::option::{core::option::Option<T>}::unwrap]:
     Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/option.rs', lines 932:4-932:34 *)
 val core_option_Option_unwrap
   (t : Type0) : option t -> state -> result (state & t)
diff --git a/tests/fstar/misc/Loops.Funs.fst b/tests/fstar/misc/Loops.Funs.fst
index d2ac5561..88389300 100644
--- a/tests/fstar/misc/Loops.Funs.fst
+++ b/tests/fstar/misc/Loops.Funs.fst
@@ -7,22 +7,22 @@ include Loops.Clauses
 
 #set-options "--z3rlimit 50 --fuel 1 --ifuel 1"
 
-(** [loops::sum]: loop 0: forward function
+(** [loops::sum]: loop 0:
     Source: 'src/loops.rs', lines 4:0-14:1 *)
 let rec sum_loop
   (max : u32) (i : u32) (s : u32) :
   Tot (result u32) (decreases (sum_loop_decreases max i s))
   =
   if i < max
-  then let* s0 = u32_add s i in let* i0 = u32_add i 1 in sum_loop max i0 s0
+  then let* s1 = u32_add s i in let* i1 = u32_add i 1 in sum_loop max i1 s1
   else u32_mul s 2
 
-(** [loops::sum]: forward function
+(** [loops::sum]:
     Source: 'src/loops.rs', lines 4:0-4:27 *)
 let sum (max : u32) : result u32 =
   sum_loop max 0 0
 
-(** [loops::sum_with_mut_borrows]: loop 0: forward function
+(** [loops::sum_with_mut_borrows]: loop 0:
     Source: 'src/loops.rs', lines 19:0-31:1 *)
 let rec sum_with_mut_borrows_loop
   (max : u32) (mi : u32) (ms : u32) :
@@ -30,17 +30,17 @@ let rec sum_with_mut_borrows_loop
   =
   if mi < max
   then
-    let* ms0 = u32_add ms mi in
-    let* mi0 = u32_add mi 1 in
-    sum_with_mut_borrows_loop max mi0 ms0
+    let* ms1 = u32_add ms mi in
+    let* mi1 = u32_add mi 1 in
+    sum_with_mut_borrows_loop max mi1 ms1
   else u32_mul ms 2
 
-(** [loops::sum_with_mut_borrows]: forward function
+(** [loops::sum_with_mut_borrows]:
     Source: 'src/loops.rs', lines 19:0-19:44 *)
 let sum_with_mut_borrows (max : u32) : result u32 =
   sum_with_mut_borrows_loop max 0 0
 
-(** [loops::sum_with_shared_borrows]: loop 0: forward function
+(** [loops::sum_with_shared_borrows]: loop 0:
     Source: 'src/loops.rs', lines 34:0-48:1 *)
 let rec sum_with_shared_borrows_loop
   (max : u32) (i : u32) (s : u32) :
@@ -48,40 +48,39 @@ let rec sum_with_shared_borrows_loop
   =
   if i < max
   then
-    let* i0 = u32_add i 1 in
-    let* s0 = u32_add s i0 in
-    sum_with_shared_borrows_loop max i0 s0
+    let* i1 = u32_add i 1 in
+    let* s1 = u32_add s i1 in
+    sum_with_shared_borrows_loop max i1 s1
   else u32_mul s 2
 
-(** [loops::sum_with_shared_borrows]: forward function
+(** [loops::sum_with_shared_borrows]:
     Source: 'src/loops.rs', lines 34:0-34:47 *)
 let sum_with_shared_borrows (max : u32) : result u32 =
   sum_with_shared_borrows_loop max 0 0
 
-(** [loops::clear]: loop 0: merged forward/backward function
-    (there is a single backward function, and the forward function returns ())
+(** [loops::clear]: loop 0:
     Source: 'src/loops.rs', lines 52:0-58:1 *)
 let rec clear_loop
   (v : alloc_vec_Vec u32) (i : usize) :
   Tot (result (alloc_vec_Vec u32)) (decreases (clear_loop_decreases v i))
   =
-  let i0 = alloc_vec_Vec_len u32 v in
-  if i < i0
+  let i1 = alloc_vec_Vec_len u32 v in
+  if i < i1
   then
-    let* i1 = usize_add i 1 in
-    let* v0 =
-      alloc_vec_Vec_index_mut_back u32 usize
-        (core_slice_index_SliceIndexUsizeSliceTInst u32) v i 0 in
-    clear_loop v0 i1
+    let* (_, index_mut_back) =
+      alloc_vec_Vec_index_mut u32 usize
+        (core_slice_index_SliceIndexUsizeSliceTInst u32) v i in
+    let* i2 = usize_add i 1 in
+    let* v1 = index_mut_back 0 in
+    clear_loop v1 i2
   else Return v
 
-(** [loops::clear]: merged forward/backward function
-    (there is a single backward function, and the forward function returns ())
+(** [loops::clear]:
     Source: 'src/loops.rs', lines 52:0-52:30 *)
 let clear (v : alloc_vec_Vec u32) : result (alloc_vec_Vec u32) =
   clear_loop v 0
 
-(** [loops::list_mem]: loop 0: forward function
+(** [loops::list_mem]: loop 0:
     Source: 'src/loops.rs', lines 66:0-75:1 *)
 let rec list_mem_loop
   (x : u32) (ls : list_t u32) :
@@ -92,54 +91,39 @@ let rec list_mem_loop
   | List_Nil -> Return false
   end
 
-(** [loops::list_mem]: forward function
+(** [loops::list_mem]:
     Source: 'src/loops.rs', lines 66:0-66:52 *)
 let list_mem (x : u32) (ls : list_t u32) : result bool =
   list_mem_loop x ls
 
-(** [loops::list_nth_mut_loop]: loop 0: forward function
+(** [loops::list_nth_mut_loop]: loop 0:
     Source: 'src/loops.rs', lines 78:0-88:1 *)
 let rec list_nth_mut_loop_loop
   (t : Type0) (ls : list_t t) (i : u32) :
-  Tot (result t) (decreases (list_nth_mut_loop_loop_decreases t ls i))
+  Tot (result (t & (t -> result (list_t t))))
+  (decreases (list_nth_mut_loop_loop_decreases t ls i))
   =
   begin match ls with
   | List_Cons x tl ->
     if i = 0
-    then Return x
-    else let* i0 = u32_sub i 1 in list_nth_mut_loop_loop t tl i0
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_loop]: forward function
-    Source: 'src/loops.rs', lines 78:0-78:71 *)
-let list_nth_mut_loop (t : Type0) (ls : list_t t) (i : u32) : result t =
-  list_nth_mut_loop_loop t ls i
-
-(** [loops::list_nth_mut_loop]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 78:0-88:1 *)
-let rec list_nth_mut_loop_loop_back
-  (t : Type0) (ls : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t)) (decreases (list_nth_mut_loop_loop_decreases t ls i))
-  =
-  begin match ls with
-  | List_Cons x tl ->
-    if i = 0
-    then Return (List_Cons ret tl)
+    then let back = fun ret -> Return (List_Cons ret tl) in Return (x, back)
     else
-      let* i0 = u32_sub i 1 in
-      let* tl0 = list_nth_mut_loop_loop_back t tl i0 ret in
-      Return (List_Cons x tl0)
+      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)
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_mut_loop]: backward function 0
+(** [loops::list_nth_mut_loop]:
     Source: 'src/loops.rs', lines 78:0-78:71 *)
-let list_nth_mut_loop_back
-  (t : Type0) (ls : list_t t) (i : u32) (ret : t) : result (list_t t) =
-  list_nth_mut_loop_loop_back t ls i ret
+let list_nth_mut_loop
+  (t : Type0) (ls : list_t t) (i : u32) :
+  result (t & (t -> result (list_t t)))
+  =
+  let* (x, back) = list_nth_mut_loop_loop t ls i in Return (x, back)
 
-(** [loops::list_nth_shared_loop]: loop 0: forward function
+(** [loops::list_nth_shared_loop]: loop 0:
     Source: 'src/loops.rs', lines 91:0-101:1 *)
 let rec list_nth_shared_loop_loop
   (t : Type0) (ls : list_t t) (i : u32) :
@@ -149,63 +133,47 @@ let rec list_nth_shared_loop_loop
   | List_Cons x tl ->
     if i = 0
     then Return x
-    else let* i0 = u32_sub i 1 in list_nth_shared_loop_loop t tl i0
+    else let* i1 = u32_sub i 1 in list_nth_shared_loop_loop t tl i1
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_shared_loop]: forward function
+(** [loops::list_nth_shared_loop]:
     Source: 'src/loops.rs', lines 91:0-91:66 *)
 let list_nth_shared_loop (t : Type0) (ls : list_t t) (i : u32) : result t =
   list_nth_shared_loop_loop t ls i
 
-(** [loops::get_elem_mut]: loop 0: forward function
+(** [loops::get_elem_mut]: loop 0:
     Source: 'src/loops.rs', lines 103:0-117:1 *)
 let rec get_elem_mut_loop
   (x : usize) (ls : list_t usize) :
-  Tot (result usize) (decreases (get_elem_mut_loop_decreases x ls))
-  =
-  begin match ls with
-  | List_Cons y tl -> if y = x then Return y else get_elem_mut_loop x tl
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::get_elem_mut]: forward function
-    Source: 'src/loops.rs', lines 103:0-103:73 *)
-let get_elem_mut
-  (slots : alloc_vec_Vec (list_t usize)) (x : usize) : result usize =
-  let* l =
-    alloc_vec_Vec_index_mut (list_t usize) usize
-      (core_slice_index_SliceIndexUsizeSliceTInst (list_t usize)) slots 0 in
-  get_elem_mut_loop x l
-
-(** [loops::get_elem_mut]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 103:0-117:1 *)
-let rec get_elem_mut_loop_back
-  (x : usize) (ls : list_t usize) (ret : usize) :
-  Tot (result (list_t usize)) (decreases (get_elem_mut_loop_decreases x ls))
+  Tot (result (usize & (usize -> result (list_t usize))))
+  (decreases (get_elem_mut_loop_decreases x ls))
   =
   begin match ls with
   | List_Cons y tl ->
     if y = x
-    then Return (List_Cons ret tl)
-    else let* tl0 = get_elem_mut_loop_back x tl ret in Return (List_Cons y tl0)
+    then let back = fun ret -> Return (List_Cons ret tl) in Return (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)
   | List_Nil -> Fail Failure
   end
 
-(** [loops::get_elem_mut]: backward function 0
+(** [loops::get_elem_mut]:
     Source: 'src/loops.rs', lines 103:0-103:73 *)
-let get_elem_mut_back
-  (slots : alloc_vec_Vec (list_t usize)) (x : usize) (ret : usize) :
-  result (alloc_vec_Vec (list_t usize))
+let get_elem_mut
+  (slots : alloc_vec_Vec (list_t usize)) (x : usize) :
+  result (usize & (usize -> result (alloc_vec_Vec (list_t usize))))
   =
-  let* l =
+  let* (l, index_mut_back) =
     alloc_vec_Vec_index_mut (list_t usize) usize
       (core_slice_index_SliceIndexUsizeSliceTInst (list_t usize)) slots 0 in
-  let* l0 = get_elem_mut_loop_back x l ret in
-  alloc_vec_Vec_index_mut_back (list_t usize) usize
-    (core_slice_index_SliceIndexUsizeSliceTInst (list_t usize)) slots 0 l0
+  let* (i, back) = get_elem_mut_loop x l in
+  let back1 = fun ret -> let* l1 = back ret in index_mut_back l1 in
+  Return (i, back1)
 
-(** [loops::get_elem_shared]: loop 0: forward function
+(** [loops::get_elem_shared]: loop 0:
     Source: 'src/loops.rs', lines 119:0-133:1 *)
 let rec get_elem_shared_loop
   (x : usize) (ls : list_t usize) :
@@ -216,7 +184,7 @@ let rec get_elem_shared_loop
   | List_Nil -> Fail Failure
   end
 
-(** [loops::get_elem_shared]: forward function
+(** [loops::get_elem_shared]:
     Source: 'src/loops.rs', lines 119:0-119:68 *)
 let get_elem_shared
   (slots : alloc_vec_Vec (list_t usize)) (x : usize) : result usize =
@@ -225,69 +193,50 @@ let get_elem_shared
       (core_slice_index_SliceIndexUsizeSliceTInst (list_t usize)) slots 0 in
   get_elem_shared_loop x l
 
-(** [loops::id_mut]: forward function
-    Source: 'src/loops.rs', lines 135:0-135:50 *)
-let id_mut (t : Type0) (ls : list_t t) : result (list_t t) =
-  Return ls
-
-(** [loops::id_mut]: backward function 0
+(** [loops::id_mut]:
     Source: 'src/loops.rs', lines 135:0-135:50 *)
-let id_mut_back
-  (t : Type0) (ls : list_t t) (ret : list_t t) : result (list_t t) =
-  Return ret
+let id_mut
+  (t : Type0) (ls : list_t t) :
+  result ((list_t t) & (list_t t -> result (list_t t)))
+  =
+  Return (ls, Return)
 
-(** [loops::id_shared]: forward function
+(** [loops::id_shared]:
     Source: 'src/loops.rs', lines 139:0-139:45 *)
 let id_shared (t : Type0) (ls : list_t t) : result (list_t t) =
   Return ls
 
-(** [loops::list_nth_mut_loop_with_id]: loop 0: forward function
+(** [loops::list_nth_mut_loop_with_id]: loop 0:
     Source: 'src/loops.rs', lines 144:0-155:1 *)
 let rec list_nth_mut_loop_with_id_loop
   (t : Type0) (i : u32) (ls : list_t t) :
-  Tot (result t) (decreases (list_nth_mut_loop_with_id_loop_decreases t i ls))
-  =
-  begin match ls with
-  | List_Cons x tl ->
-    if i = 0
-    then Return x
-    else let* i0 = u32_sub i 1 in list_nth_mut_loop_with_id_loop t i0 tl
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_loop_with_id]: forward function
-    Source: 'src/loops.rs', lines 144:0-144:75 *)
-let list_nth_mut_loop_with_id
-  (t : Type0) (ls : list_t t) (i : u32) : result t =
-  let* ls0 = id_mut t ls in list_nth_mut_loop_with_id_loop t i ls0
-
-(** [loops::list_nth_mut_loop_with_id]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 144:0-155:1 *)
-let rec list_nth_mut_loop_with_id_loop_back
-  (t : Type0) (i : u32) (ls : list_t t) (ret : t) :
-  Tot (result (list_t t))
+  Tot (result (t & (t -> result (list_t t))))
   (decreases (list_nth_mut_loop_with_id_loop_decreases t i ls))
   =
   begin match ls with
   | List_Cons x tl ->
     if i = 0
-    then Return (List_Cons ret tl)
+    then let back = fun ret -> Return (List_Cons ret tl) in Return (x, back)
     else
-      let* i0 = u32_sub i 1 in
-      let* tl0 = list_nth_mut_loop_with_id_loop_back t i0 tl ret in
-      Return (List_Cons x tl0)
+      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)
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_mut_loop_with_id]: backward function 0
+(** [loops::list_nth_mut_loop_with_id]:
     Source: 'src/loops.rs', lines 144:0-144:75 *)
-let list_nth_mut_loop_with_id_back
-  (t : Type0) (ls : list_t t) (i : u32) (ret : t) : result (list_t t) =
-  let* ls0 = id_mut t ls in
-  let* l = list_nth_mut_loop_with_id_loop_back t i ls0 ret in
-  id_mut_back t ls l
+let list_nth_mut_loop_with_id
+  (t : Type0) (ls : list_t t) (i : u32) :
+  result (t & (t -> result (list_t t)))
+  =
+  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)
 
-(** [loops::list_nth_shared_loop_with_id]: loop 0: forward function
+(** [loops::list_nth_shared_loop_with_id]: loop 0:
     Source: 'src/loops.rs', lines 158:0-169:1 *)
 let rec list_nth_shared_loop_with_id_loop
   (t : Type0) (i : u32) (ls : list_t t) :
@@ -298,46 +247,21 @@ let rec list_nth_shared_loop_with_id_loop
   | List_Cons x tl ->
     if i = 0
     then Return x
-    else let* i0 = u32_sub i 1 in list_nth_shared_loop_with_id_loop t i0 tl
+    else let* i1 = u32_sub i 1 in list_nth_shared_loop_with_id_loop t i1 tl
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_shared_loop_with_id]: forward function
+(** [loops::list_nth_shared_loop_with_id]:
     Source: 'src/loops.rs', lines 158:0-158:70 *)
 let list_nth_shared_loop_with_id
   (t : Type0) (ls : list_t t) (i : u32) : result t =
-  let* ls0 = id_shared t ls in list_nth_shared_loop_with_id_loop t i ls0
+  let* ls1 = id_shared t ls in list_nth_shared_loop_with_id_loop t i ls1
 
-(** [loops::list_nth_mut_loop_pair]: loop 0: forward function
+(** [loops::list_nth_mut_loop_pair]: loop 0:
     Source: 'src/loops.rs', lines 174:0-195:1 *)
 let rec list_nth_mut_loop_pair_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
-  Tot (result (t & t))
-  (decreases (list_nth_mut_loop_pair_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then Return (x0, x1)
-      else let* i0 = u32_sub i 1 in list_nth_mut_loop_pair_loop t tl0 tl1 i0
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_loop_pair]: forward function
-    Source: 'src/loops.rs', lines 174:0-178:27 *)
-let list_nth_mut_loop_pair
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
-  list_nth_mut_loop_pair_loop t ls0 ls1 i
-
-(** [loops::list_nth_mut_loop_pair]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 174:0-195:1 *)
-let rec list_nth_mut_loop_pair_loop_back'a
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t))
+  Tot (result ((t & t) & (t -> result (list_t t)) & (t -> result (list_t t))))
   (decreases (list_nth_mut_loop_pair_loop_decreases t ls0 ls1 i))
   =
   begin match ls0 with
@@ -345,55 +269,34 @@ let rec list_nth_mut_loop_pair_loop_back'a
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (List_Cons ret tl0)
+      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)
       else
-        let* i0 = u32_sub i 1 in
-        let* tl00 = list_nth_mut_loop_pair_loop_back'a t tl0 tl1 i0 ret in
-        Return (List_Cons x0 tl00)
+        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
+        let back_'b1 =
+          fun ret -> let* tl11 = back_'b ret in Return (List_Cons x1 tl11) in
+        Return (p, back_'a1, back_'b1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_mut_loop_pair]: backward function 0
+(** [loops::list_nth_mut_loop_pair]:
     Source: 'src/loops.rs', lines 174:0-178:27 *)
-let list_nth_mut_loop_pair_back'a
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  result (list_t t)
-  =
-  list_nth_mut_loop_pair_loop_back'a t ls0 ls1 i ret
-
-(** [loops::list_nth_mut_loop_pair]: loop 0: backward function 1
-    Source: 'src/loops.rs', lines 174:0-195:1 *)
-let rec list_nth_mut_loop_pair_loop_back'b
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t))
-  (decreases (list_nth_mut_loop_pair_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then Return (List_Cons ret tl1)
-      else
-        let* i0 = u32_sub i 1 in
-        let* tl10 = list_nth_mut_loop_pair_loop_back'b t tl0 tl1 i0 ret in
-        Return (List_Cons x1 tl10)
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_loop_pair]: backward function 1
-    Source: 'src/loops.rs', lines 174:0-178:27 *)
-let list_nth_mut_loop_pair_back'b
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  result (list_t t)
+let list_nth_mut_loop_pair
+  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
+  result ((t & t) & (t -> result (list_t t)) & (t -> result (list_t t)))
   =
-  list_nth_mut_loop_pair_loop_back'b t ls0 ls1 i ret
+  let* (p, back_'a, back_'b) = list_nth_mut_loop_pair_loop t ls0 ls1 i in
+  Return (p, back_'a, back_'b)
 
-(** [loops::list_nth_shared_loop_pair]: loop 0: forward function
+(** [loops::list_nth_shared_loop_pair]: loop 0:
     Source: 'src/loops.rs', lines 198:0-219:1 *)
 let rec list_nth_shared_loop_pair_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
@@ -406,23 +309,23 @@ let rec list_nth_shared_loop_pair_loop
     | List_Cons x1 tl1 ->
       if i = 0
       then Return (x0, x1)
-      else let* i0 = u32_sub i 1 in list_nth_shared_loop_pair_loop t tl0 tl1 i0
+      else let* i1 = u32_sub i 1 in list_nth_shared_loop_pair_loop t tl0 tl1 i1
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_shared_loop_pair]: forward function
+(** [loops::list_nth_shared_loop_pair]:
     Source: 'src/loops.rs', lines 198:0-202:19 *)
 let list_nth_shared_loop_pair
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
   list_nth_shared_loop_pair_loop t ls0 ls1 i
 
-(** [loops::list_nth_mut_loop_pair_merge]: loop 0: forward function
+(** [loops::list_nth_mut_loop_pair_merge]: loop 0:
     Source: 'src/loops.rs', lines 223:0-238:1 *)
 let rec list_nth_mut_loop_pair_merge_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
-  Tot (result (t & t))
+  Tot (result ((t & t) & ((t & t) -> result ((list_t t) & (list_t t)))))
   (decreases (list_nth_mut_loop_pair_merge_loop_decreases t ls0 ls1 i))
   =
   begin match ls0 with
@@ -430,52 +333,34 @@ let rec list_nth_mut_loop_pair_merge_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then
+        let back_'a =
+          fun ret ->
+            let (x, x2) = ret in Return (List_Cons x tl0, List_Cons x2 tl1) in
+        Return ((x0, x1), back_'a)
       else
-        let* i0 = u32_sub i 1 in list_nth_mut_loop_pair_merge_loop t tl0 tl1 i0
+        let* i1 = u32_sub i 1 in
+        let* (p, back_'a) = list_nth_mut_loop_pair_merge_loop t tl0 tl1 i1 in
+        let back_'a1 =
+          fun ret ->
+            let* (tl01, tl11) = back_'a ret in
+            Return (List_Cons x0 tl01, List_Cons x1 tl11) in
+        Return (p, back_'a1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_mut_loop_pair_merge]: forward function
+(** [loops::list_nth_mut_loop_pair_merge]:
     Source: 'src/loops.rs', lines 223:0-227:27 *)
 let list_nth_mut_loop_pair_merge
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
-  list_nth_mut_loop_pair_merge_loop t ls0 ls1 i
-
-(** [loops::list_nth_mut_loop_pair_merge]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 223:0-238:1 *)
-let rec list_nth_mut_loop_pair_merge_loop_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : (t & t)) :
-  Tot (result ((list_t t) & (list_t t)))
-  (decreases (list_nth_mut_loop_pair_merge_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then let (x, x2) = ret in Return (List_Cons x tl0, List_Cons x2 tl1)
-      else
-        let* i0 = u32_sub i 1 in
-        let* (tl00, tl10) =
-          list_nth_mut_loop_pair_merge_loop_back t tl0 tl1 i0 ret in
-        Return (List_Cons x0 tl00, List_Cons x1 tl10)
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_loop_pair_merge]: backward function 0
-    Source: 'src/loops.rs', lines 223:0-227:27 *)
-let list_nth_mut_loop_pair_merge_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : (t & t)) :
-  result ((list_t t) & (list_t t))
+  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
+  result ((t & t) & ((t & t) -> result ((list_t t) & (list_t t))))
   =
-  list_nth_mut_loop_pair_merge_loop_back t ls0 ls1 i ret
+  let* (p, back_'a) = list_nth_mut_loop_pair_merge_loop t ls0 ls1 i in
+  Return (p, back_'a)
 
-(** [loops::list_nth_shared_loop_pair_merge]: loop 0: forward function
+(** [loops::list_nth_shared_loop_pair_merge]: loop 0:
     Source: 'src/loops.rs', lines 241:0-256:1 *)
 let rec list_nth_shared_loop_pair_merge_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
@@ -489,24 +374,24 @@ let rec list_nth_shared_loop_pair_merge_loop
       if i = 0
       then Return (x0, x1)
       else
-        let* i0 = u32_sub i 1 in
-        list_nth_shared_loop_pair_merge_loop t tl0 tl1 i0
+        let* i1 = u32_sub i 1 in
+        list_nth_shared_loop_pair_merge_loop t tl0 tl1 i1
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_shared_loop_pair_merge]: forward function
+(** [loops::list_nth_shared_loop_pair_merge]:
     Source: 'src/loops.rs', lines 241:0-245:19 *)
 let list_nth_shared_loop_pair_merge
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
   list_nth_shared_loop_pair_merge_loop t ls0 ls1 i
 
-(** [loops::list_nth_mut_shared_loop_pair]: loop 0: forward function
+(** [loops::list_nth_mut_shared_loop_pair]: loop 0:
     Source: 'src/loops.rs', lines 259:0-274:1 *)
 let rec list_nth_mut_shared_loop_pair_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
-  Tot (result (t & t))
+  Tot (result ((t & t) & (t -> result (list_t t))))
   (decreases (list_nth_mut_shared_loop_pair_loop_decreases t ls0 ls1 i))
   =
   begin match ls0 with
@@ -514,56 +399,34 @@ let rec list_nth_mut_shared_loop_pair_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then
+        let back_'a = fun ret -> Return (List_Cons ret tl0) in
+        Return ((x0, x1), back_'a)
       else
-        let* i0 = u32_sub i 1 in
-        list_nth_mut_shared_loop_pair_loop t tl0 tl1 i0
+        let* i1 = u32_sub i 1 in
+        let* (p, back_'a) = list_nth_mut_shared_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
+        Return (p, back_'a1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_mut_shared_loop_pair]: forward function
+(** [loops::list_nth_mut_shared_loop_pair]:
     Source: 'src/loops.rs', lines 259:0-263:23 *)
 let list_nth_mut_shared_loop_pair
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
-  list_nth_mut_shared_loop_pair_loop t ls0 ls1 i
-
-(** [loops::list_nth_mut_shared_loop_pair]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 259:0-274:1 *)
-let rec list_nth_mut_shared_loop_pair_loop_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t))
-  (decreases (list_nth_mut_shared_loop_pair_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then Return (List_Cons ret tl0)
-      else
-        let* i0 = u32_sub i 1 in
-        let* tl00 = list_nth_mut_shared_loop_pair_loop_back t tl0 tl1 i0 ret in
-        Return (List_Cons x0 tl00)
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_shared_loop_pair]: backward function 0
-    Source: 'src/loops.rs', lines 259:0-263:23 *)
-let list_nth_mut_shared_loop_pair_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  result (list_t t)
+  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
+  result ((t & t) & (t -> result (list_t t)))
   =
-  list_nth_mut_shared_loop_pair_loop_back t ls0 ls1 i ret
+  let* (p, back_'a) = list_nth_mut_shared_loop_pair_loop t ls0 ls1 i in
+  Return (p, back_'a)
 
-(** [loops::list_nth_mut_shared_loop_pair_merge]: loop 0: forward function
+(** [loops::list_nth_mut_shared_loop_pair_merge]: loop 0:
     Source: 'src/loops.rs', lines 278:0-293:1 *)
 let rec list_nth_mut_shared_loop_pair_merge_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
-  Tot (result (t & t))
+  Tot (result ((t & t) & (t -> result (list_t t))))
   (decreases (list_nth_mut_shared_loop_pair_merge_loop_decreases t ls0 ls1 i))
   =
   begin match ls0 with
@@ -571,57 +434,35 @@ let rec list_nth_mut_shared_loop_pair_merge_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then
+        let back_'a = fun ret -> Return (List_Cons ret tl0) in
+        Return ((x0, x1), back_'a)
       else
-        let* i0 = u32_sub i 1 in
-        list_nth_mut_shared_loop_pair_merge_loop t tl0 tl1 i0
+        let* i1 = u32_sub i 1 in
+        let* (p, back_'a) =
+          list_nth_mut_shared_loop_pair_merge_loop t tl0 tl1 i1 in
+        let back_'a1 =
+          fun ret -> let* tl01 = back_'a ret in Return (List_Cons x0 tl01) in
+        Return (p, back_'a1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_mut_shared_loop_pair_merge]: forward function
+(** [loops::list_nth_mut_shared_loop_pair_merge]:
     Source: 'src/loops.rs', lines 278:0-282:23 *)
 let list_nth_mut_shared_loop_pair_merge
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
-  list_nth_mut_shared_loop_pair_merge_loop t ls0 ls1 i
-
-(** [loops::list_nth_mut_shared_loop_pair_merge]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 278:0-293:1 *)
-let rec list_nth_mut_shared_loop_pair_merge_loop_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t))
-  (decreases (list_nth_mut_shared_loop_pair_merge_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then Return (List_Cons ret tl0)
-      else
-        let* i0 = u32_sub i 1 in
-        let* tl00 =
-          list_nth_mut_shared_loop_pair_merge_loop_back t tl0 tl1 i0 ret in
-        Return (List_Cons x0 tl00)
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_mut_shared_loop_pair_merge]: backward function 0
-    Source: 'src/loops.rs', lines 278:0-282:23 *)
-let list_nth_mut_shared_loop_pair_merge_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  result (list_t t)
+  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
+  result ((t & t) & (t -> result (list_t t)))
   =
-  list_nth_mut_shared_loop_pair_merge_loop_back t ls0 ls1 i ret
+  let* (p, back_'a) = list_nth_mut_shared_loop_pair_merge_loop t ls0 ls1 i in
+  Return (p, back_'a)
 
-(** [loops::list_nth_shared_mut_loop_pair]: loop 0: forward function
+(** [loops::list_nth_shared_mut_loop_pair]: loop 0:
     Source: 'src/loops.rs', lines 297:0-312:1 *)
 let rec list_nth_shared_mut_loop_pair_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
-  Tot (result (t & t))
+  Tot (result ((t & t) & (t -> result (list_t t))))
   (decreases (list_nth_shared_mut_loop_pair_loop_decreases t ls0 ls1 i))
   =
   begin match ls0 with
@@ -629,56 +470,34 @@ let rec list_nth_shared_mut_loop_pair_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then
+        let back_'b = fun ret -> Return (List_Cons ret tl1) in
+        Return ((x0, x1), back_'b)
       else
-        let* i0 = u32_sub i 1 in
-        list_nth_shared_mut_loop_pair_loop t tl0 tl1 i0
+        let* i1 = u32_sub i 1 in
+        let* (p, back_'b) = list_nth_shared_mut_loop_pair_loop t tl0 tl1 i1 in
+        let back_'b1 =
+          fun ret -> let* tl11 = back_'b ret in Return (List_Cons x1 tl11) in
+        Return (p, back_'b1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_shared_mut_loop_pair]: forward function
+(** [loops::list_nth_shared_mut_loop_pair]:
     Source: 'src/loops.rs', lines 297:0-301:23 *)
 let list_nth_shared_mut_loop_pair
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
-  list_nth_shared_mut_loop_pair_loop t ls0 ls1 i
-
-(** [loops::list_nth_shared_mut_loop_pair]: loop 0: backward function 1
-    Source: 'src/loops.rs', lines 297:0-312:1 *)
-let rec list_nth_shared_mut_loop_pair_loop_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t))
-  (decreases (list_nth_shared_mut_loop_pair_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then Return (List_Cons ret tl1)
-      else
-        let* i0 = u32_sub i 1 in
-        let* tl10 = list_nth_shared_mut_loop_pair_loop_back t tl0 tl1 i0 ret in
-        Return (List_Cons x1 tl10)
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_shared_mut_loop_pair]: backward function 1
-    Source: 'src/loops.rs', lines 297:0-301:23 *)
-let list_nth_shared_mut_loop_pair_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  result (list_t t)
+  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
+  result ((t & t) & (t -> result (list_t t)))
   =
-  list_nth_shared_mut_loop_pair_loop_back t ls0 ls1 i ret
+  let* (p, back_'b) = list_nth_shared_mut_loop_pair_loop t ls0 ls1 i in
+  Return (p, back_'b)
 
-(** [loops::list_nth_shared_mut_loop_pair_merge]: loop 0: forward function
+(** [loops::list_nth_shared_mut_loop_pair_merge]: loop 0:
     Source: 'src/loops.rs', lines 316:0-331:1 *)
 let rec list_nth_shared_mut_loop_pair_merge_loop
   (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
-  Tot (result (t & t))
+  Tot (result ((t & t) & (t -> result (list_t t))))
   (decreases (list_nth_shared_mut_loop_pair_merge_loop_decreases t ls0 ls1 i))
   =
   begin match ls0 with
@@ -686,49 +505,27 @@ let rec list_nth_shared_mut_loop_pair_merge_loop
     begin match ls1 with
     | List_Cons x1 tl1 ->
       if i = 0
-      then Return (x0, x1)
+      then
+        let back_'a = fun ret -> Return (List_Cons ret tl1) in
+        Return ((x0, x1), back_'a)
       else
-        let* i0 = u32_sub i 1 in
-        list_nth_shared_mut_loop_pair_merge_loop t tl0 tl1 i0
+        let* i1 = u32_sub i 1 in
+        let* (p, back_'a) =
+          list_nth_shared_mut_loop_pair_merge_loop t tl0 tl1 i1 in
+        let back_'a1 =
+          fun ret -> let* tl11 = back_'a ret in Return (List_Cons x1 tl11) in
+        Return (p, back_'a1)
     | List_Nil -> Fail Failure
     end
   | List_Nil -> Fail Failure
   end
 
-(** [loops::list_nth_shared_mut_loop_pair_merge]: forward function
+(** [loops::list_nth_shared_mut_loop_pair_merge]:
     Source: 'src/loops.rs', lines 316:0-320:23 *)
 let list_nth_shared_mut_loop_pair_merge
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) : result (t & t) =
-  list_nth_shared_mut_loop_pair_merge_loop t ls0 ls1 i
-
-(** [loops::list_nth_shared_mut_loop_pair_merge]: loop 0: backward function 0
-    Source: 'src/loops.rs', lines 316:0-331:1 *)
-let rec list_nth_shared_mut_loop_pair_merge_loop_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  Tot (result (list_t t))
-  (decreases (list_nth_shared_mut_loop_pair_merge_loop_decreases t ls0 ls1 i))
-  =
-  begin match ls0 with
-  | List_Cons x0 tl0 ->
-    begin match ls1 with
-    | List_Cons x1 tl1 ->
-      if i = 0
-      then Return (List_Cons ret tl1)
-      else
-        let* i0 = u32_sub i 1 in
-        let* tl10 =
-          list_nth_shared_mut_loop_pair_merge_loop_back t tl0 tl1 i0 ret in
-        Return (List_Cons x1 tl10)
-    | List_Nil -> Fail Failure
-    end
-  | List_Nil -> Fail Failure
-  end
-
-(** [loops::list_nth_shared_mut_loop_pair_merge]: backward function 0
-    Source: 'src/loops.rs', lines 316:0-320:23 *)
-let list_nth_shared_mut_loop_pair_merge_back
-  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) (ret : t) :
-  result (list_t t)
+  (t : Type0) (ls0 : list_t t) (ls1 : list_t t) (i : u32) :
+  result ((t & t) & (t -> result (list_t t)))
   =
-  list_nth_shared_mut_loop_pair_merge_loop_back t ls0 ls1 i ret
+  let* (p, back_'a) = list_nth_shared_mut_loop_pair_merge_loop t ls0 ls1 i in
+  Return (p, back_'a)
 
diff --git a/tests/fstar/misc/NoNestedBorrows.fst b/tests/fstar/misc/NoNestedBorrows.fst
index 1386b02c..ffcc32f3 100644
--- a/tests/fstar/misc/NoNestedBorrows.fst
+++ b/tests/fstar/misc/NoNestedBorrows.fst
@@ -37,96 +37,96 @@ type sum_t (t1 t2 : Type0) =
 | Sum_Left : t1 -> sum_t t1 t2
 | Sum_Right : t2 -> sum_t t1 t2
 
-(** [no_nested_borrows::neg_test]: forward function
+(** [no_nested_borrows::neg_test]:
     Source: 'src/no_nested_borrows.rs', lines 48:0-48:30 *)
 let neg_test (x : i32) : result i32 =
   i32_neg x
 
-(** [no_nested_borrows::add_u32]: forward function
+(** [no_nested_borrows::add_u32]:
     Source: 'src/no_nested_borrows.rs', lines 54:0-54:37 *)
 let add_u32 (x : u32) (y : u32) : result u32 =
   u32_add x y
 
-(** [no_nested_borrows::subs_u32]: forward function
+(** [no_nested_borrows::subs_u32]:
     Source: 'src/no_nested_borrows.rs', lines 60:0-60:38 *)
 let subs_u32 (x : u32) (y : u32) : result u32 =
   u32_sub x y
 
-(** [no_nested_borrows::div_u32]: forward function
+(** [no_nested_borrows::div_u32]:
     Source: 'src/no_nested_borrows.rs', lines 66:0-66:37 *)
 let div_u32 (x : u32) (y : u32) : result u32 =
   u32_div x y
 
-(** [no_nested_borrows::div_u32_const]: forward function
+(** [no_nested_borrows::div_u32_const]:
     Source: 'src/no_nested_borrows.rs', lines 73:0-73:35 *)
 let div_u32_const (x : u32) : result u32 =
   u32_div x 2
 
-(** [no_nested_borrows::rem_u32]: forward function
+(** [no_nested_borrows::rem_u32]:
     Source: 'src/no_nested_borrows.rs', lines 78:0-78:37 *)
 let rem_u32 (x : u32) (y : u32) : result u32 =
   u32_rem x y
 
-(** [no_nested_borrows::mul_u32]: forward function
+(** [no_nested_borrows::mul_u32]:
     Source: 'src/no_nested_borrows.rs', lines 82:0-82:37 *)
 let mul_u32 (x : u32) (y : u32) : result u32 =
   u32_mul x y
 
-(** [no_nested_borrows::add_i32]: forward function
+(** [no_nested_borrows::add_i32]:
     Source: 'src/no_nested_borrows.rs', lines 88:0-88:37 *)
 let add_i32 (x : i32) (y : i32) : result i32 =
   i32_add x y
 
-(** [no_nested_borrows::subs_i32]: forward function
+(** [no_nested_borrows::subs_i32]:
     Source: 'src/no_nested_borrows.rs', lines 92:0-92:38 *)
 let subs_i32 (x : i32) (y : i32) : result i32 =
   i32_sub x y
 
-(** [no_nested_borrows::div_i32]: forward function
+(** [no_nested_borrows::div_i32]:
     Source: 'src/no_nested_borrows.rs', lines 96:0-96:37 *)
 let div_i32 (x : i32) (y : i32) : result i32 =
   i32_div x y
 
-(** [no_nested_borrows::div_i32_const]: forward function
+(** [no_nested_borrows::div_i32_const]:
     Source: 'src/no_nested_borrows.rs', lines 100:0-100:35 *)
 let div_i32_const (x : i32) : result i32 =
   i32_div x 2
 
-(** [no_nested_borrows::rem_i32]: forward function
+(** [no_nested_borrows::rem_i32]:
     Source: 'src/no_nested_borrows.rs', lines 104:0-104:37 *)
 let rem_i32 (x : i32) (y : i32) : result i32 =
   i32_rem x y
 
-(** [no_nested_borrows::mul_i32]: forward function
+(** [no_nested_borrows::mul_i32]:
     Source: 'src/no_nested_borrows.rs', lines 108:0-108:37 *)
 let mul_i32 (x : i32) (y : i32) : result i32 =
   i32_mul x y
 
-(** [no_nested_borrows::mix_arith_u32]: forward function
+(** [no_nested_borrows::mix_arith_u32]:
     Source: 'src/no_nested_borrows.rs', lines 112:0-112:51 *)
 let mix_arith_u32 (x : u32) (y : u32) (z : u32) : result u32 =
   let* i = u32_add x y in
-  let* i0 = u32_div x y in
-  let* i1 = u32_mul i i0 in
-  let* i2 = u32_rem z y in
-  let* i3 = u32_sub x i2 in
-  let* i4 = u32_add i1 i3 in
-  let* i5 = u32_add x y in
-  let* i6 = u32_add i5 z in
-  u32_rem i4 i6
-
-(** [no_nested_borrows::mix_arith_i32]: forward function
+  let* i1 = u32_div x y in
+  let* i2 = u32_mul i i1 in
+  let* i3 = u32_rem z y in
+  let* i4 = u32_sub x i3 in
+  let* i5 = u32_add i2 i4 in
+  let* i6 = u32_add x y in
+  let* i7 = u32_add i6 z in
+  u32_rem i5 i7
+
+(** [no_nested_borrows::mix_arith_i32]:
     Source: 'src/no_nested_borrows.rs', lines 116:0-116:51 *)
 let mix_arith_i32 (x : i32) (y : i32) (z : i32) : result i32 =
   let* i = i32_add x y in
-  let* i0 = i32_div x y in
-  let* i1 = i32_mul i i0 in
-  let* i2 = i32_rem z y in
-  let* i3 = i32_sub x i2 in
-  let* i4 = i32_add i1 i3 in
-  let* i5 = i32_add x y in
-  let* i6 = i32_add i5 z in
-  i32_rem i4 i6
+  let* i1 = i32_div x y in
+  let* i2 = i32_mul i i1 in
+  let* i3 = i32_rem z y in
+  let* i4 = i32_sub x i3 in
+  let* i5 = i32_add i2 i4 in
+  let* i6 = i32_add x y in
+  let* i7 = i32_add i6 z in
+  i32_rem i5 i7
 
 (** [no_nested_borrows::CONST0]
     Source: 'src/no_nested_borrows.rs', lines 125:0-125:23 *)
@@ -138,22 +138,22 @@ let const0_c : usize = eval_global const0_body
 let const1_body : result usize = usize_mul 2 2
 let const1_c : usize = eval_global const1_body
 
-(** [no_nested_borrows::cast_u32_to_i32]: forward function
+(** [no_nested_borrows::cast_u32_to_i32]:
     Source: 'src/no_nested_borrows.rs', lines 128:0-128:37 *)
 let cast_u32_to_i32 (x : u32) : result i32 =
   scalar_cast U32 I32 x
 
-(** [no_nested_borrows::cast_bool_to_i32]: forward function
+(** [no_nested_borrows::cast_bool_to_i32]:
     Source: 'src/no_nested_borrows.rs', lines 132:0-132:39 *)
 let cast_bool_to_i32 (x : bool) : result i32 =
   scalar_cast_bool I32 x
 
-(** [no_nested_borrows::cast_bool_to_bool]: forward function
+(** [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
 
-(** [no_nested_borrows::test2]: forward function
+(** [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 ()
@@ -161,12 +161,12 @@ let test2 : result unit =
 (** Unit test for [no_nested_borrows::test2] *)
 let _ = assert_norm (test2 = Return ())
 
-(** [no_nested_borrows::get_max]: forward function
+(** [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
 
-(** [no_nested_borrows::test3]: forward function
+(** [no_nested_borrows::test3]:
     Source: 'src/no_nested_borrows.rs', lines 162:0-162:14 *)
 let test3 : result unit =
   let* x = get_max 4 3 in
@@ -177,7 +177,7 @@ let test3 : result unit =
 (** Unit test for [no_nested_borrows::test3] *)
 let _ = assert_norm (test3 = Return ())
 
-(** [no_nested_borrows::test_neg1]: forward function
+(** [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 ()
@@ -185,7 +185,7 @@ let test_neg1 : result unit =
 (** Unit test for [no_nested_borrows::test_neg1] *)
 let _ = assert_norm (test_neg1 = Return ())
 
-(** [no_nested_borrows::refs_test1]: forward function
+(** [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 ()
@@ -193,7 +193,7 @@ let refs_test1 : result unit =
 (** Unit test for [no_nested_borrows::refs_test1] *)
 let _ = assert_norm (refs_test1 = Return ())
 
-(** [no_nested_borrows::refs_test2]: forward function
+(** [no_nested_borrows::refs_test2]:
     Source: 'src/no_nested_borrows.rs', lines 187:0-187:19 *)
 let refs_test2 : result unit =
   if not (2 = 2)
@@ -209,7 +209,7 @@ let refs_test2 : result unit =
 (** Unit test for [no_nested_borrows::refs_test2] *)
 let _ = assert_norm (refs_test2 = Return ())
 
-(** [no_nested_borrows::test_list1]: forward function
+(** [no_nested_borrows::test_list1]:
     Source: 'src/no_nested_borrows.rs', lines 203:0-203:19 *)
 let test_list1 : result unit =
   Return ()
@@ -217,33 +217,33 @@ let test_list1 : result unit =
 (** Unit test for [no_nested_borrows::test_list1] *)
 let _ = assert_norm (test_list1 = Return ())
 
-(** [no_nested_borrows::test_box1]: forward function
+(** [no_nested_borrows::test_box1]:
     Source: 'src/no_nested_borrows.rs', lines 208:0-208:18 *)
 let test_box1 : result unit =
-  let b = 0 in
-  let* b0 = alloc_boxed_Box_deref_mut_back i32 b 1 in
-  let* x = alloc_boxed_Box_deref i32 b0 in
+  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 ()
 
 (** Unit test for [no_nested_borrows::test_box1] *)
 let _ = assert_norm (test_box1 = Return ())
 
-(** [no_nested_borrows::copy_int]: forward function
+(** [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
 
-(** [no_nested_borrows::test_unreachable]: forward function
+(** [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 ()
 
-(** [no_nested_borrows::test_panic]: forward function
+(** [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 ()
 
-(** [no_nested_borrows::test_copy_int]: forward function
+(** [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 ()
@@ -251,25 +251,24 @@ let test_copy_int : result unit =
 (** Unit test for [no_nested_borrows::test_copy_int] *)
 let _ = assert_norm (test_copy_int = Return ())
 
-(** [no_nested_borrows::is_cons]: forward function
+(** [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 x l0 -> Return true
+  | List_Cons _ _ -> Return true
   | List_Nil -> Return false
   end
 
-(** [no_nested_borrows::test_is_cons]: forward function
+(** [no_nested_borrows::test_is_cons]:
     Source: 'src/no_nested_borrows.rs', lines 253:0-253:21 *)
 let test_is_cons : result unit =
-  let l = List_Nil in
-  let* b = is_cons i32 (List_Cons 0 l) in
+  let* b = is_cons i32 (List_Cons 0 List_Nil) in
   if not b then Fail Failure else Return ()
 
 (** Unit test for [no_nested_borrows::test_is_cons] *)
 let _ = assert_norm (test_is_cons = Return ())
 
-(** [no_nested_borrows::split_list]: forward function
+(** [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
@@ -277,37 +276,33 @@ let split_list (t : Type0) (l : list_t t) : result (t & (list_t t)) =
   | List_Nil -> Fail Failure
   end
 
-(** [no_nested_borrows::test_split_list]: forward function
+(** [no_nested_borrows::test_split_list]:
     Source: 'src/no_nested_borrows.rs', lines 267:0-267:24 *)
 let test_split_list : result unit =
-  let l = List_Nil in
-  let* p = split_list i32 (List_Cons 0 l) in
+  let* p = split_list i32 (List_Cons 0 List_Nil) in
   let (hd, _) = p in
   if not (hd = 0) then Fail Failure else Return ()
 
 (** Unit test for [no_nested_borrows::test_split_list] *)
 let _ = assert_norm (test_split_list = Return ())
 
-(** [no_nested_borrows::choose]: forward function
+(** [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 =
-  if b then Return x else Return y
+let choose
+  (t : Type0) (b : bool) (x : t) (y : t) : result (t & (t -> result (t & t))) =
+  if b
+  then let back_'a = fun ret -> Return (ret, y) in Return (x, back_'a)
+  else let back_'a = fun ret -> Return (x, ret) in Return (y, back_'a)
 
-(** [no_nested_borrows::choose]: backward function 0
-    Source: 'src/no_nested_borrows.rs', lines 274:0-274:70 *)
-let choose_back
-  (t : Type0) (b : bool) (x : t) (y : t) (ret : t) : result (t & t) =
-  if b then Return (ret, y) else Return (x, ret)
-
-(** [no_nested_borrows::choose_test]: forward function
+(** [no_nested_borrows::choose_test]:
     Source: 'src/no_nested_borrows.rs', lines 282:0-282:20 *)
 let choose_test : result unit =
-  let* z = choose i32 true 0 0 in
-  let* z0 = i32_add z 1 in
-  if not (z0 = 1)
+  let* (z, choose_back) = choose i32 true 0 0 in
+  let* z1 = i32_add z 1 in
+  if not (z1 = 1)
   then Fail Failure
   else
-    let* (x, y) = choose_back i32 true 0 0 z0 in
+    let* (x, y) = choose_back z1 in
     if not (x = 1)
     then Fail Failure
     else if not (y = 0) then Fail Failure else Return ()
@@ -315,7 +310,7 @@ let choose_test : result unit =
 (** Unit test for [no_nested_borrows::choose_test] *)
 let _ = assert_norm (choose_test = Return ())
 
-(** [no_nested_borrows::test_char]: forward function
+(** [no_nested_borrows::test_char]:
     Source: 'src/no_nested_borrows.rs', lines 294:0-294:26 *)
 let test_char : result char =
   Return 'a'
@@ -332,50 +327,47 @@ and nodeElem_t (t : Type0) =
 | NodeElem_Cons : tree_t t -> nodeElem_t t -> nodeElem_t t
 | NodeElem_Nil : nodeElem_t t
 
-(** [no_nested_borrows::list_length]: forward function
+(** [no_nested_borrows::list_length]:
     Source: 'src/no_nested_borrows.rs', lines 339:0-339:48 *)
 let rec list_length (t : Type0) (l : list_t t) : result u32 =
   begin match l with
-  | List_Cons x l1 -> let* i = list_length t l1 in u32_add 1 i
+  | List_Cons _ l1 -> let* i = list_length t l1 in u32_add 1 i
   | List_Nil -> Return 0
   end
 
-(** [no_nested_borrows::list_nth_shared]: forward function
+(** [no_nested_borrows::list_nth_shared]:
     Source: 'src/no_nested_borrows.rs', lines 347:0-347:62 *)
 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* i0 = u32_sub i 1 in list_nth_shared t tl i0
-  | List_Nil -> Fail Failure
-  end
-
-(** [no_nested_borrows::list_nth_mut]: forward function
-    Source: 'src/no_nested_borrows.rs', lines 363:0-363:67 *)
-let rec list_nth_mut (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* i0 = u32_sub i 1 in list_nth_mut t tl i0
+    else let* i1 = u32_sub i 1 in list_nth_shared t tl i1
   | List_Nil -> Fail Failure
   end
 
-(** [no_nested_borrows::list_nth_mut]: backward function 0
+(** [no_nested_borrows::list_nth_mut]:
     Source: 'src/no_nested_borrows.rs', lines 363:0-363:67 *)
-let rec list_nth_mut_back
-  (t : Type0) (l : list_t t) (i : u32) (ret : t) : result (list_t t) =
+let rec list_nth_mut
+  (t : Type0) (l : list_t t) (i : u32) :
+  result (t & (t -> result (list_t t)))
+  =
   begin match l with
   | List_Cons x tl ->
     if i = 0
-    then Return (List_Cons ret tl)
+    then
+      let back_'a = fun ret -> Return (List_Cons ret tl) in Return (x, back_'a)
     else
-      let* i0 = u32_sub i 1 in
-      let* tl0 = list_nth_mut_back t tl i0 ret in
-      Return (List_Cons x tl0)
+      let* i1 = u32_sub i 1 in
+      let* (x1, list_nth_mut_back) = list_nth_mut t tl i1 in
+      let back_'a =
+        fun ret -> let* tl1 = list_nth_mut_back ret in Return (List_Cons x tl1)
+        in
+      Return (x1, back_'a)
   | List_Nil -> Fail Failure
   end
 
-(** [no_nested_borrows::list_rev_aux]: forward function
+(** [no_nested_borrows::list_rev_aux]:
     Source: 'src/no_nested_borrows.rs', lines 379:0-379:63 *)
 let rec list_rev_aux
   (t : Type0) (li : list_t t) (lo : list_t t) : result (list_t t) =
@@ -384,120 +376,99 @@ let rec list_rev_aux
   | List_Nil -> Return lo
   end
 
-(** [no_nested_borrows::list_rev]: merged forward/backward function
-    (there is a single backward function, and the forward function returns ())
+(** [no_nested_borrows::list_rev]:
     Source: 'src/no_nested_borrows.rs', lines 393:0-393:42 *)
 let list_rev (t : Type0) (l : list_t t) : result (list_t t) =
-  let li = core_mem_replace (list_t t) l List_Nil in list_rev_aux t li List_Nil
+  let (li, _) = core_mem_replace (list_t t) l List_Nil in
+  list_rev_aux t li List_Nil
 
-(** [no_nested_borrows::test_list_functions]: forward function
+(** [no_nested_borrows::test_list_functions]:
     Source: 'src/no_nested_borrows.rs', lines 398:0-398:28 *)
 let test_list_functions : result unit =
-  let l = List_Nil in
-  let l0 = List_Cons 2 l in
-  let l1 = List_Cons 1 l0 in
+  let l = List_Cons 2 List_Nil in
+  let l1 = List_Cons 1 l in
   let* i = list_length i32 (List_Cons 0 l1) in
   if not (i = 3)
   then Fail Failure
   else
-    let* i0 = list_nth_shared i32 (List_Cons 0 l1) 0 in
-    if not (i0 = 0)
+    let* i1 = list_nth_shared i32 (List_Cons 0 l1) 0 in
+    if not (i1 = 0)
     then Fail Failure
     else
-      let* i1 = list_nth_shared i32 (List_Cons 0 l1) 1 in
-      if not (i1 = 1)
+      let* i2 = list_nth_shared i32 (List_Cons 0 l1) 1 in
+      if not (i2 = 1)
       then Fail Failure
       else
-        let* i2 = list_nth_shared i32 (List_Cons 0 l1) 2 in
-        if not (i2 = 2)
+        let* i3 = list_nth_shared i32 (List_Cons 0 l1) 2 in
+        if not (i3 = 2)
         then Fail Failure
         else
-          let* ls = list_nth_mut_back i32 (List_Cons 0 l1) 1 3 in
-          let* i3 = list_nth_shared i32 ls 0 in
-          if not (i3 = 0)
+          let* (_, list_nth_mut_back) = list_nth_mut i32 (List_Cons 0 l1) 1 in
+          let* ls = list_nth_mut_back 3 in
+          let* i4 = list_nth_shared i32 ls 0 in
+          if not (i4 = 0)
           then Fail Failure
           else
-            let* i4 = list_nth_shared i32 ls 1 in
-            if not (i4 = 3)
+            let* i5 = list_nth_shared i32 ls 1 in
+            if not (i5 = 3)
             then Fail Failure
             else
-              let* i5 = list_nth_shared i32 ls 2 in
-              if not (i5 = 2) then Fail Failure else Return ()
+              let* i6 = list_nth_shared i32 ls 2 in
+              if not (i6 = 2) then Fail Failure else Return ()
 
 (** Unit test for [no_nested_borrows::test_list_functions] *)
 let _ = assert_norm (test_list_functions = Return ())
 
-(** [no_nested_borrows::id_mut_pair1]: forward function
+(** [no_nested_borrows::id_mut_pair1]:
     Source: 'src/no_nested_borrows.rs', lines 414:0-414:89 *)
-let id_mut_pair1 (t1 t2 : Type0) (x : t1) (y : t2) : result (t1 & t2) =
-  Return (x, y)
-
-(** [no_nested_borrows::id_mut_pair1]: backward function 0
-    Source: 'src/no_nested_borrows.rs', lines 414:0-414:89 *)
-let id_mut_pair1_back
-  (t1 t2 : Type0) (x : t1) (y : t2) (ret : (t1 & t2)) : result (t1 & t2) =
-  let (x0, x1) = ret in Return (x0, x1)
-
-(** [no_nested_borrows::id_mut_pair2]: forward function
+let id_mut_pair1
+  (t1 t2 : Type0) (x : t1) (y : t2) :
+  result ((t1 & t2) & ((t1 & t2) -> result (t1 & t2)))
+  =
+  let back_'a = fun ret -> let (x1, x2) = ret in Return (x1, x2) in
+  Return ((x, y), back_'a)
+
+(** [no_nested_borrows::id_mut_pair2]:
     Source: 'src/no_nested_borrows.rs', lines 418:0-418:88 *)
-let id_mut_pair2 (t1 t2 : Type0) (p : (t1 & t2)) : result (t1 & t2) =
-  let (x, x0) = p in Return (x, x0)
-
-(** [no_nested_borrows::id_mut_pair2]: backward function 0
-    Source: 'src/no_nested_borrows.rs', lines 418:0-418:88 *)
-let id_mut_pair2_back
-  (t1 t2 : Type0) (p : (t1 & t2)) (ret : (t1 & t2)) : result (t1 & t2) =
-  let (x, x0) = ret in Return (x, x0)
-
-(** [no_nested_borrows::id_mut_pair3]: forward function
+let id_mut_pair2
+  (t1 t2 : Type0) (p : (t1 & t2)) :
+  result ((t1 & t2) & ((t1 & t2) -> result (t1 & t2)))
+  =
+  let (x, x1) = p in
+  let back_'a = fun ret -> let (x2, x3) = ret in Return (x2, x3) in
+  Return ((x, x1), back_'a)
+
+(** [no_nested_borrows::id_mut_pair3]:
     Source: 'src/no_nested_borrows.rs', lines 422:0-422:93 *)
-let id_mut_pair3 (t1 t2 : Type0) (x : t1) (y : t2) : result (t1 & t2) =
-  Return (x, y)
-
-(** [no_nested_borrows::id_mut_pair3]: backward function 0
-    Source: 'src/no_nested_borrows.rs', lines 422:0-422:93 *)
-let id_mut_pair3_back'a
-  (t1 t2 : Type0) (x : t1) (y : t2) (ret : t1) : result t1 =
-  Return ret
-
-(** [no_nested_borrows::id_mut_pair3]: backward function 1
-    Source: 'src/no_nested_borrows.rs', lines 422:0-422:93 *)
-let id_mut_pair3_back'b
-  (t1 t2 : Type0) (x : t1) (y : t2) (ret : t2) : result t2 =
-  Return ret
-
-(** [no_nested_borrows::id_mut_pair4]: forward function
-    Source: 'src/no_nested_borrows.rs', lines 426:0-426:92 *)
-let id_mut_pair4 (t1 t2 : Type0) (p : (t1 & t2)) : result (t1 & t2) =
-  let (x, x0) = p in Return (x, x0)
+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)
 
-(** [no_nested_borrows::id_mut_pair4]: backward function 0
+(** [no_nested_borrows::id_mut_pair4]:
     Source: 'src/no_nested_borrows.rs', lines 426:0-426:92 *)
-let id_mut_pair4_back'a
-  (t1 t2 : Type0) (p : (t1 & t2)) (ret : t1) : result t1 =
-  Return ret
-
-(** [no_nested_borrows::id_mut_pair4]: backward function 1
-    Source: 'src/no_nested_borrows.rs', lines 426:0-426:92 *)
-let id_mut_pair4_back'b
-  (t1 t2 : Type0) (p : (t1 & t2)) (ret : t2) : result t2 =
-  Return ret
+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)
 
 (** [no_nested_borrows::StructWithTuple]
     Source: 'src/no_nested_borrows.rs', lines 433:0-433:34 *)
 type structWithTuple_t (t1 t2 : Type0) = { p : (t1 & t2); }
 
-(** [no_nested_borrows::new_tuple1]: forward function
+(** [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) }
 
-(** [no_nested_borrows::new_tuple2]: forward function
+(** [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) }
 
-(** [no_nested_borrows::new_tuple3]: forward function
+(** [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) }
@@ -506,12 +477,12 @@ let new_tuple3 : result (structWithTuple_t u64 i64) =
     Source: 'src/no_nested_borrows.rs', lines 450:0-450:33 *)
 type structWithPair_t (t1 t2 : Type0) = { p : pair_t t1 t2; }
 
-(** [no_nested_borrows::new_pair1]: forward function
+(** [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 } }
 
-(** [no_nested_borrows::test_constants]: forward function
+(** [no_nested_borrows::test_constants]:
     Source: 'src/no_nested_borrows.rs', lines 462:0-462:23 *)
 let test_constants : result unit =
   let* swt = new_tuple1 in
@@ -519,14 +490,14 @@ let test_constants : result unit =
   if not (i = 1)
   then Fail Failure
   else
-    let* swt0 = new_tuple2 in
-    let (i0, _) = swt0.p in
-    if not (i0 = 1)
+    let* swt1 = new_tuple2 in
+    let (i1, _) = swt1.p in
+    if not (i1 = 1)
     then Fail Failure
     else
-      let* swt1 = new_tuple3 in
-      let (i1, _) = swt1.p in
-      if not (i1 = 1)
+      let* swt2 = new_tuple3 in
+      let (i2, _) = swt2.p in
+      if not (i2 = 1)
       then Fail Failure
       else
         let* swp = new_pair1 in
@@ -535,7 +506,7 @@ let test_constants : result unit =
 (** Unit test for [no_nested_borrows::test_constants] *)
 let _ = assert_norm (test_constants = Return ())
 
-(** [no_nested_borrows::test_weird_borrows1]: forward function
+(** [no_nested_borrows::test_weird_borrows1]:
     Source: 'src/no_nested_borrows.rs', lines 471:0-471:28 *)
 let test_weird_borrows1 : result unit =
   Return ()
@@ -543,59 +514,72 @@ let test_weird_borrows1 : result unit =
 (** Unit test for [no_nested_borrows::test_weird_borrows1] *)
 let _ = assert_norm (test_weird_borrows1 = Return ())
 
-(** [no_nested_borrows::test_mem_replace]: merged forward/backward function
-    (there is a single backward function, and the forward function returns ())
+(** [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
+  let (y, _) = core_mem_replace u32 px 1 in
   if not (y = 0) then Fail Failure else Return 2
 
-(** [no_nested_borrows::test_shared_borrow_bool1]: forward function
+(** [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
 
-(** [no_nested_borrows::test_shared_borrow_bool2]: forward function
+(** [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
 
-(** [no_nested_borrows::test_shared_borrow_enum1]: forward function
+(** [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 i l0 -> Return 1 | List_Nil -> Return 0 end
+  begin match l with | List_Cons _ _ -> Return 1 | List_Nil -> Return 0 end
 
-(** [no_nested_borrows::test_shared_borrow_enum2]: forward function
+(** [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
 
-(** [no_nested_borrows::Tuple]
+(** [no_nested_borrows::incr]:
     Source: 'src/no_nested_borrows.rs', lines 539:0-539:24 *)
+let incr (x : u32) : result u32 =
+  u32_add x 1
+
+(** [no_nested_borrows::call_incr]:
+    Source: 'src/no_nested_borrows.rs', lines 543:0-543:35 *)
+let call_incr (x : u32) : result u32 =
+  incr x
+
+(** [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)
+
+(** [no_nested_borrows::Tuple]
+    Source: 'src/no_nested_borrows.rs', lines 554:0-554:24 *)
 type tuple_t (t1 t2 : Type0) = t1 * t2
 
-(** [no_nested_borrows::use_tuple_struct]: merged forward/backward function
-    (there is a single backward function, and the forward function returns ())
-    Source: 'src/no_nested_borrows.rs', lines 541:0-541:48 *)
+(** [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)
 
-(** [no_nested_borrows::create_tuple_struct]: forward function
-    Source: 'src/no_nested_borrows.rs', lines 545:0-545:61 *)
+(** [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)
 
 (** [no_nested_borrows::IdType]
-    Source: 'src/no_nested_borrows.rs', lines 550:0-550:20 *)
+    Source: 'src/no_nested_borrows.rs', lines 565:0-565:20 *)
 type idType_t (t : Type0) = t
 
-(** [no_nested_borrows::use_id_type]: forward function
-    Source: 'src/no_nested_borrows.rs', lines 552:0-552:40 *)
+(** [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
 
-(** [no_nested_borrows::create_id_type]: forward function
-    Source: 'src/no_nested_borrows.rs', lines 556:0-556:43 *)
+(** [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
 
diff --git a/tests/fstar/misc/Paper.fst b/tests/fstar/misc/Paper.fst
index 14bc59e8..cf4dc454 100644
--- a/tests/fstar/misc/Paper.fst
+++ b/tests/fstar/misc/Paper.fst
@@ -5,40 +5,36 @@ open Primitives
 
 #set-options "--z3rlimit 50 --fuel 1 --ifuel 1"
 
-(** [paper::ref_incr]: merged forward/backward function
-    (there is a single backward function, and the forward function returns ())
+(** [paper::ref_incr]:
     Source: 'src/paper.rs', lines 4:0-4:28 *)
 let ref_incr (x : i32) : result i32 =
   i32_add x 1
 
-(** [paper::test_incr]: forward function
+(** [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* i = ref_incr 0 in if not (i = 1) then Fail Failure else Return ()
 
 (** Unit test for [paper::test_incr] *)
 let _ = assert_norm (test_incr = Return ())
 
-(** [paper::choose]: forward function
+(** [paper::choose]:
     Source: 'src/paper.rs', lines 15:0-15:70 *)
-let choose (t : Type0) (b : bool) (x : t) (y : t) : result t =
-  if b then Return x else Return y
+let choose
+  (t : Type0) (b : bool) (x : t) (y : t) : result (t & (t -> result (t & t))) =
+  if b
+  then let back_'a = fun ret -> Return (ret, y) in Return (x, back_'a)
+  else let back_'a = fun ret -> Return (x, ret) in Return (y, back_'a)
 
-(** [paper::choose]: backward function 0
-    Source: 'src/paper.rs', lines 15:0-15:70 *)
-let choose_back
-  (t : Type0) (b : bool) (x : t) (y : t) (ret : t) : result (t & t) =
-  if b then Return (ret, y) else Return (x, ret)
-
-(** [paper::test_choose]: forward function
+(** [paper::test_choose]:
     Source: 'src/paper.rs', lines 23:0-23:20 *)
 let test_choose : result unit =
-  let* z = choose i32 true 0 0 in
-  let* z0 = i32_add z 1 in
-  if not (z0 = 1)
+  let* (z, choose_back) = choose i32 true 0 0 in
+  let* z1 = i32_add z 1 in
+  if not (z1 = 1)
   then Fail Failure
   else
-    let* (x, y) = choose_back i32 true 0 0 z0 in
+    let* (x, y) = choose_back z1 in
     if not (x = 1)
     then Fail Failure
     else if not (y = 0) then Fail Failure else Return ()
@@ -52,31 +48,28 @@ type list_t (t : Type0) =
 | List_Cons : t -> list_t t -> list_t t
 | List_Nil : list_t t
 
-(** [paper::list_nth_mut]: forward function
-    Source: 'src/paper.rs', lines 42:0-42:67 *)
-let rec list_nth_mut (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* i0 = u32_sub i 1 in list_nth_mut t tl i0
-  | List_Nil -> Fail Failure
-  end
-
-(** [paper::list_nth_mut]: backward function 0
+(** [paper::list_nth_mut]:
     Source: 'src/paper.rs', lines 42:0-42:67 *)
-let rec list_nth_mut_back
-  (t : Type0) (l : list_t t) (i : u32) (ret : t) : result (list_t t) =
+let rec list_nth_mut
+  (t : Type0) (l : list_t t) (i : u32) :
+  result (t & (t -> result (list_t t)))
+  =
   begin match l with
   | List_Cons x tl ->
     if i = 0
-    then Return (List_Cons ret tl)
+    then
+      let back_'a = fun ret -> Return (List_Cons ret tl) in Return (x, back_'a)
     else
-      let* i0 = u32_sub i 1 in
-      let* tl0 = list_nth_mut_back t tl i0 ret in
-      Return (List_Cons x tl0)
+      let* i1 = u32_sub i 1 in
+      let* (x1, list_nth_mut_back) = list_nth_mut t tl i1 in
+      let back_'a =
+        fun ret -> let* tl1 = list_nth_mut_back ret in Return (List_Cons x tl1)
+        in
+      Return (x1, back_'a)
   | List_Nil -> Fail Failure
   end
 
-(** [paper::sum]: forward function
+(** [paper::sum]:
     Source: 'src/paper.rs', lines 57:0-57:32 *)
 let rec sum (l : list_t i32) : result i32 =
   begin match l with
@@ -84,27 +77,26 @@ let rec sum (l : list_t i32) : result i32 =
   | List_Nil -> Return 0
   end
 
-(** [paper::test_nth]: forward function
+(** [paper::test_nth]:
     Source: 'src/paper.rs', lines 68:0-68:17 *)
 let test_nth : result unit =
-  let l = List_Nil in
-  let l0 = List_Cons 3 l in
-  let l1 = List_Cons 2 l0 in
-  let* x = list_nth_mut i32 (List_Cons 1 l1) 2 in
-  let* x0 = i32_add x 1 in
-  let* l2 = list_nth_mut_back i32 (List_Cons 1 l1) 2 x0 in
+  let l = List_Cons 3 List_Nil in
+  let l1 = List_Cons 2 l in
+  let* (x, list_nth_mut_back) = list_nth_mut i32 (List_Cons 1 l1) 2 in
+  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 ()
 
 (** Unit test for [paper::test_nth] *)
 let _ = assert_norm (test_nth = Return ())
 
-(** [paper::call_choose]: forward function
+(** [paper::call_choose]:
     Source: 'src/paper.rs', lines 76:0-76:44 *)
 let call_choose (p : (u32 & u32)) : result u32 =
   let (px, py) = p in
-  let* pz = choose u32 true px py in
-  let* pz0 = u32_add pz 1 in
-  let* (px0, _) = choose_back u32 true px py pz0 in
-  Return px0
+  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
 
diff --git a/tests/fstar/misc/PoloniusList.fst b/tests/fstar/misc/PoloniusList.fst
index 188b22d8..b477802b 100644
--- a/tests/fstar/misc/PoloniusList.fst
+++ b/tests/fstar/misc/PoloniusList.fst
@@ -11,24 +11,22 @@ type list_t (t : Type0) =
 | List_Cons : t -> list_t t -> list_t t
 | List_Nil : list_t t
 
-(** [polonius_list::get_list_at_x]: forward function
+(** [polonius_list::get_list_at_x]:
     Source: 'src/polonius_list.rs', lines 13:0-13:76 *)
-let rec get_list_at_x (ls : list_t u32) (x : u32) : result (list_t u32) =
-  begin match ls with
-  | List_Cons hd tl ->
-    if hd = x then Return (List_Cons hd tl) else get_list_at_x tl x
-  | List_Nil -> Return List_Nil
-  end
-
-(** [polonius_list::get_list_at_x]: backward function 0
-    Source: 'src/polonius_list.rs', lines 13:0-13:76 *)
-let rec get_list_at_x_back
-  (ls : list_t u32) (x : u32) (ret : list_t u32) : result (list_t u32) =
+let rec get_list_at_x
+  (ls : list_t u32) (x : u32) :
+  result ((list_t u32) & (list_t u32 -> result (list_t u32)))
+  =
   begin match ls with
   | List_Cons hd tl ->
     if hd = x
-    then Return ret
-    else let* tl0 = get_list_at_x_back tl x ret in Return (List_Cons hd tl0)
-  | List_Nil -> Return ret
+    then Return (List_Cons hd tl, Return)
+    else
+      let* (l, get_list_at_x_back) = get_list_at_x tl x in
+      let back_'a =
+        fun ret ->
+          let* tl1 = get_list_at_x_back ret in Return (List_Cons hd tl1) in
+      Return (l, back_'a)
+  | List_Nil -> Return (List_Nil, Return)
   end
 
diff --git a/tests/fstar/misc/Primitives.fst b/tests/fstar/misc/Primitives.fst
index a3ffbde4..fca80829 100644
--- a/tests/fstar/misc/Primitives.fst
+++ b/tests/fstar/misc/Primitives.fst
@@ -55,8 +55,7 @@ type string = string
 let is_zero (n: nat) : bool = n = 0
 let decrease (n: nat{n > 0}) : nat = n - 1
 
-let core_mem_replace (a : Type0) (x : a) (y : a) : a = x
-let core_mem_replace_back (a : Type0) (x : a) (y : a) : a = y
+let core_mem_replace (a : Type0) (x : a) (y : a) : a & a = (x, x)
 
 // We don't really use raw pointers for now
 type mut_raw_ptr (t : Type0) = { v : t }
@@ -477,8 +476,7 @@ noeq type core_ops_index_Index (self idx : Type0) = {
 // Trait declaration: [core::ops::index::IndexMut]
 noeq type core_ops_index_IndexMut (self idx : Type0) = {
   indexInst : core_ops_index_Index self idx;
-  index_mut : self → idx → result indexInst.output;
-  index_mut_back : self → idx → indexInst.output → result self;
+  index_mut : self → idx → result (indexInst.output & (indexInst.output → result self));
 }
 
 // Trait declaration [core::ops::deref::Deref]
@@ -490,8 +488,7 @@ noeq type core_ops_deref_Deref (self : Type0) = {
 // Trait declaration [core::ops::deref::DerefMut]
 noeq type core_ops_deref_DerefMut (self : Type0) = {
   derefInst : core_ops_deref_Deref self;
-  deref_mut : self → result derefInst.target;
-  deref_mut_back : self → derefInst.target → result self;
+  deref_mut : self → result (derefInst.target & (derefInst.target → result self));
 }
 
 type core_ops_range_Range (a : Type0) = {
@@ -502,8 +499,8 @@ 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_mut (t : Type0) (x : t) : result t = Return x
-let alloc_boxed_Box_deref_mut_back (t : Type) (_ : t) (x : t) : result t = Return x
+let alloc_boxed_Box_deref_mut (t : Type0) (x : t) : result (t & (t -> result t)) =
+  Return (x, (fun x -> Return x))
 
 // Trait instance
 let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self = {
@@ -515,7 +512,6 @@ let alloc_boxed_Box_coreopsDerefInst (self : Type0) : core_ops_deref_Deref self
 let alloc_boxed_Box_coreopsDerefMutInst (self : Type0) : core_ops_deref_DerefMut self = {
   derefInst = alloc_boxed_Box_coreopsDerefInst self;
   deref_mut = alloc_boxed_Box_deref_mut self;
-  deref_mut_back = alloc_boxed_Box_deref_mut_back self;
 }
 
 (*** Array *)
@@ -535,10 +531,18 @@ let array_index_usize (a : Type0) (n : usize) (x : array a n) (i : usize) : resu
   if i < length x then Return (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) =
+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)
   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)
+
 (*** Slice *)
 type slice (a : Type0) = s:list a{length s <= usize_max}
 
@@ -552,6 +556,13 @@ let slice_update_usize (a : Type0) (x : slice a) (i : usize) (nx : a) : result (
   if i < length x then Return (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)
+
 (*** Subslices *)
 
 let array_to_slice (a : Type0) (n : usize) (x : array a n) : result (slice a) = Return x
@@ -559,6 +570,10 @@ let array_from_slice (a : Type0) (n : usize) (x : array a n) (s : slice a) : res
   if length s = n then Return 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)
+
 // 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) =
   admit()
@@ -588,8 +603,13 @@ let alloc_vec_Vec_index_usize (#a : Type0) (v : alloc_vec_Vec a) (i : usize) : r
 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
 
-// The **forward** function shouldn't be used
-let alloc_vec_Vec_push_fwd (a  : Type0) (v : alloc_vec_Vec a) (x : a) : unit = ()
+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)
+  | Fail e -> Fail e
+
 let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
   Pure (result (alloc_vec_Vec a))
   (requires True)
@@ -605,9 +625,6 @@ let alloc_vec_Vec_push (a  : Type0) (v : alloc_vec_Vec a) (x : a) :
     end
   else Fail Failure
 
-// The **forward** function shouldn't be used
-let alloc_vec_Vec_insert_fwd (a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) : result unit =
-  if i < length v then Return () 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
 
@@ -619,13 +636,11 @@ noeq type core_slice_index_SliceIndex (self t : Type0) = {
   sealedInst : core_slice_index_private_slice_index_Sealed self;
   output : Type0;
   get : self → t → result (option output);
-  get_mut : self → t → result (option output);
-  get_mut_back : self → t → option output → result t;
+  get_mut : self → t → result (option output & (option output -> result t));
   get_unchecked : self → const_raw_ptr t → result (const_raw_ptr output);
   get_unchecked_mut : self → mut_raw_ptr t → result (mut_raw_ptr output);
   index : self → t → result output;
-  index_mut : self → t → result output;
-  index_mut_back : self → t → output → result t;
+  index_mut : self → t → result (output & (output -> result t));
 }
 
 // [core::slice::index::[T]::index]: forward function
@@ -643,14 +658,8 @@ let core_slice_index_RangeUsize_get (t : Type0) (i : core_ops_range_Range usize)
   admit () // TODO
 
 // [core::slice::index::Range::get_mut]: forward function
-let core_slice_index_RangeUsize_get_mut
-  (t : Type0) : core_ops_range_Range usize → slice t → result (option (slice t)) =
-  admit () // TODO
-
-// [core::slice::index::Range::get_mut]: backward function 0
-let core_slice_index_RangeUsize_get_mut_back
-  (t : Type0) :
-  core_ops_range_Range usize → slice t → option (slice t) → result (slice t) =
+let core_slice_index_RangeUsize_get_mut (t : Type0) :
+  core_ops_range_Range usize → slice t → result (option (slice t) & (option (slice t) -> result (slice t))) =
   admit () // TODO
 
 // [core::slice::index::Range::get_unchecked]: forward function
@@ -675,27 +684,16 @@ let core_slice_index_RangeUsize_index
   admit () // TODO
 
 // [core::slice::index::Range::index_mut]: forward function
-let core_slice_index_RangeUsize_index_mut
-  (t : Type0) : core_ops_range_Range usize → slice t → result (slice t) =
-  admit () // TODO
-
-// [core::slice::index::Range::index_mut]: backward function 0
-let core_slice_index_RangeUsize_index_mut_back
-  (t : Type0) : core_ops_range_Range usize → slice t → slice t → result (slice t) =
+let core_slice_index_RangeUsize_index_mut (t : Type0) :
+  core_ops_range_Range usize → slice t → result (slice t & (slice t -> result (slice t))) =
   admit () // TODO
 
 // [core::slice::index::[T]::index_mut]: forward function
 let core_slice_index_Slice_index_mut
   (t idx : Type0) (inst : core_slice_index_SliceIndex idx (slice t)) :
-  slice t → idx → result inst.output =
+  slice t → idx → result (inst.output & (inst.output -> result (slice t))) =
   admit () // 
 
-// [core::slice::index::[T]::index_mut]: backward function 0
-let core_slice_index_Slice_index_mut_back
-  (t idx : Type0) (inst : core_slice_index_SliceIndex idx (slice t)) :
-  slice t → idx → inst.output → result (slice t) =
-  admit () // TODO
-
 // [core::array::[T; N]::index]: forward function
 let core_array_Array_index
   (t idx : Type0) (n : usize) (inst : core_ops_index_Index (slice t) idx)
@@ -705,13 +703,8 @@ let core_array_Array_index
 // [core::array::[T; N]::index_mut]: forward function
 let core_array_Array_index_mut
   (t idx : Type0) (n : usize) (inst : core_ops_index_IndexMut (slice t) idx)
-  (a : array t n) (i : idx) : result inst.indexInst.output =
-  admit () // TODO
-
-// [core::array::[T; N]::index_mut]: backward function 0
-let core_array_Array_index_mut_back
-  (t idx : Type0) (n : usize) (inst : core_ops_index_IndexMut (slice t) idx)
-  (a : array t n) (i : idx) (x : inst.indexInst.output) : result (array t n) =
+  (a : array t n) (i : idx) :
+  result (inst.indexInst.output & (inst.indexInst.output -> result (array t n))) =
   admit () // TODO
 
 // Trait implementation: [core::slice::index::private_slice_index::Range]
@@ -725,12 +718,10 @@ let core_slice_index_SliceIndexRangeUsizeSliceTInst (t : Type0) :
   output = slice t;
   get = core_slice_index_RangeUsize_get t;
   get_mut = core_slice_index_RangeUsize_get_mut t;
-  get_mut_back = core_slice_index_RangeUsize_get_mut_back t;
   get_unchecked = core_slice_index_RangeUsize_get_unchecked t;
   get_unchecked_mut = core_slice_index_RangeUsize_get_unchecked_mut t;
   index = core_slice_index_RangeUsize_index t;
   index_mut = core_slice_index_RangeUsize_index_mut t;
-  index_mut_back = core_slice_index_RangeUsize_index_mut_back t;
 }
 
 // Trait implementation: [core::slice::index::[T]]
@@ -747,7 +738,6 @@ let core_ops_index_IndexMutSliceTIInst (t idx : Type0)
   core_ops_index_IndexMut (slice t) idx = {
   indexInst = core_ops_index_IndexSliceTIInst t idx inst;
   index_mut = core_slice_index_Slice_index_mut t idx inst;
-  index_mut_back = core_slice_index_Slice_index_mut_back t idx inst;
 }
 
 // Trait implementation: [core::array::[T; N]]
@@ -764,7 +754,6 @@ let core_ops_index_IndexMutArrayIInst (t idx : Type0) (n : usize)
   core_ops_index_IndexMut (array t n) idx = {
   indexInst = core_ops_index_IndexArrayInst t idx n inst.indexInst;
   index_mut = core_array_Array_index_mut t idx n inst;
-  index_mut_back = core_array_Array_index_mut_back t idx n inst;
 }
 
 // [core::slice::index::usize::get]: forward function
@@ -773,13 +762,8 @@ let core_slice_index_usize_get
   admit () // TODO
 
 // [core::slice::index::usize::get_mut]: forward function
-let core_slice_index_usize_get_mut
-  (t : Type0) : usize → slice t → result (option t) =
-  admit () // TODO
-
-// [core::slice::index::usize::get_mut]: backward function 0
-let core_slice_index_usize_get_mut_back
-  (t : Type0) : usize → slice t → option t → result (slice t) =
+let core_slice_index_usize_get_mut (t : Type0) :
+  usize → slice t → result (option t & (option t -> result (slice t))) =
   admit () // TODO
 
 // [core::slice::index::usize::get_unchecked]: forward function
@@ -797,12 +781,8 @@ let core_slice_index_usize_index (t : Type0) : usize → slice t → result t =
   admit () // TODO
 
 // [core::slice::index::usize::index_mut]: forward function
-let core_slice_index_usize_index_mut (t : Type0) : usize → slice t → result t =
-  admit () // TODO
-
-// [core::slice::index::usize::index_mut]: backward function 0
-let core_slice_index_usize_index_mut_back
-  (t : Type0) : usize → slice t → t → result (slice t) =
+let core_slice_index_usize_index_mut (t : Type0) :
+  usize → slice t → result (t & (t -> result (slice t))) =
   admit () // TODO
 
 // Trait implementation: [core::slice::index::private_slice_index::usize]
@@ -816,12 +796,10 @@ let core_slice_index_SliceIndexUsizeSliceTInst (t : Type0) :
   output = t;
   get = core_slice_index_usize_get t;
   get_mut = core_slice_index_usize_get_mut t;
-  get_mut_back = core_slice_index_usize_get_mut_back t;
   get_unchecked = core_slice_index_usize_get_unchecked t;
   get_unchecked_mut = core_slice_index_usize_get_unchecked_mut t;
   index = core_slice_index_usize_index t;
   index_mut = core_slice_index_usize_index_mut t;
-  index_mut_back = core_slice_index_usize_index_mut_back t;
 }
 
 // [alloc::vec::Vec::index]: forward function
@@ -831,13 +809,8 @@ let alloc_vec_Vec_index (t idx : Type0) (inst : core_slice_index_SliceIndex idx
 
 // [alloc::vec::Vec::index_mut]: forward function
 let alloc_vec_Vec_index_mut (t idx : Type0) (inst : core_slice_index_SliceIndex idx (slice t))
-  (self : alloc_vec_Vec t) (i : idx) : result inst.output =
-  admit () // TODO
-
-// [alloc::vec::Vec::index_mut]: backward function 0
-let alloc_vec_Vec_index_mut_back
-  (t idx : Type0) (inst : core_slice_index_SliceIndex idx (slice t))
-  (self : alloc_vec_Vec t) (i : idx) (x : inst.output) : result (alloc_vec_Vec t) =
+  (self : alloc_vec_Vec t) (i : idx) :
+  result (inst.output & (inst.output -> result (alloc_vec_Vec t))) =
   admit () // TODO
 
 // Trait implementation: [alloc::vec::Vec]
@@ -854,7 +827,6 @@ let alloc_vec_Vec_coreopsindexIndexMutInst (t idx : Type0)
   core_ops_index_IndexMut (alloc_vec_Vec t) idx = {
   indexInst = alloc_vec_Vec_coreopsindexIndexInst t idx inst;
   index_mut = alloc_vec_Vec_index_mut t idx inst;
-  index_mut_back = alloc_vec_Vec_index_mut_back t idx inst;
 }
 
 (*** Theorems *)
@@ -870,15 +842,7 @@ let alloc_vec_Vec_index_eq (#a : Type0) (v : alloc_vec_Vec a) (i : usize) :
 let alloc_vec_Vec_index_mut_eq (#a : Type0) (v : alloc_vec_Vec a) (i : usize) :
   Lemma (
     alloc_vec_Vec_index_mut a usize (core_slice_index_SliceIndexUsizeSliceTInst a) v i ==
-      alloc_vec_Vec_index_usize v i)
+      alloc_vec_Vec_index_mut_usize v i)
   [SMTPat (alloc_vec_Vec_index_mut a usize (core_slice_index_SliceIndexUsizeSliceTInst a) v i)]
   =
   admit()
-
-let alloc_vec_Vec_index_mut_back_eq (#a : Type0) (v : alloc_vec_Vec a) (i : usize) (x : a) :
-  Lemma (
-    alloc_vec_Vec_index_mut_back a usize (core_slice_index_SliceIndexUsizeSliceTInst a) v i x ==
-      alloc_vec_Vec_update_usize v i x)
-  [SMTPat (alloc_vec_Vec_index_mut_back a usize (core_slice_index_SliceIndexUsizeSliceTInst a) v i x)]
-  =
-  admit()