Merge pull request #8 from jaycech3n/dev

Merge big diff on dev

8 files changed, 466 insertions, 292 deletions

diff --git a/spartan/core/Spartan.thy b/spartan/core/Spartan.thy
index 8fa6cfe..a4ad300 100644
--- a/spartan/core/Spartan.thy
+++ b/spartan/core/Spartan.thy
@@ -10,22 +10,29 @@ keywords
   "focus" "\<guillemotright>" "\<^item>" "\<^enum>" "~" :: prf_script_goal % "proof" and
   "congruence" "print_coercions" :: thy_decl and
   "rhs" "derive" "prems" "vars" :: quasi_command
-  
 
 begin
 
 
 section \<open>Prelude\<close>
 
+paragraph \<open>Set up the meta-logic just so.\<close>
+
+paragraph \<open>Notation.\<close>
+
 declare [[eta_contract=false]]
 
+text \<open>
+  Rebind notation for meta-lambdas since we want to use `\<lambda>` for the object
+  lambdas. Meta-functions now use the binder `fn`.
+\<close>
 setup \<open>
 let
   val typ = Simple_Syntax.read_typ
   fun mixfix (sy, ps, p) = Mixfix (Input.string sy, ps, p, Position.no_range)
 in
   Sign.del_syntax (Print_Mode.ASCII, true)
-    [("_lambda", typ "pttrns \<Rightarrow> 'a \<Rightarrow> logic", mixfix ("(3fn _./ _)", [0, 3], 3))]
+    [("_lambda", typ "pttrns \<Rightarrow> 'a \<Rightarrow> logic", mixfix ("(3%_./ _)", [0, 3], 3))]
   #> Sign.del_syntax Syntax.mode_default
     [("_lambda", typ "pttrns \<Rightarrow> 'a \<Rightarrow> logic", mixfix ("(3\<lambda>_./ _)", [0, 3], 3))]
   #> Sign.add_syntax Syntax.mode_default
@@ -38,11 +45,16 @@ translations "a $ b" \<rightharpoonup> "a (b)"
 
 abbreviation (input) K where "K x \<equiv> fn _. x"
 
+paragraph \<open>
+  Deeply embed dependent type theory: meta-type of expressions, and typing
+  judgment.
+\<close>
+
 typedecl o
 
 judgment has_type :: \<open>o \<Rightarrow> o \<Rightarrow> prop\<close> ("(2_:/ _)" 999)
 
-text \<open>Type annotations:\<close>
+text \<open>Type annotations for type-checking and inference.\<close>
 
 definition anno :: \<open>o \<Rightarrow> o \<Rightarrow> o\<close> ("'(_ : _')")
   where "(a : A) \<equiv> a" if "a: A"
@@ -51,7 +63,9 @@ lemma anno: "a: A \<Longrightarrow> (a : A): A"
   by (unfold anno_def)
 
 
-section \<open>Universes\<close>
+section \<open>Axioms\<close>
+
+subsection \<open>Universes\<close>
 
 typedecl lvl \<comment> \<open>Universe levels\<close>
 
@@ -65,19 +79,19 @@ axiomatization
   lt_trans: "i < j \<Longrightarrow> j < k \<Longrightarrow> i < k"
 
 axiomatization U :: \<open>lvl \<Rightarrow> o\<close> where
-  U_hierarchy: "i < j \<Longrightarrow> U i: U j" and
-  U_cumulative: "A: U i \<Longrightarrow> i < j \<Longrightarrow> A: U j"
+  Ui_in_Uj: "i < j \<Longrightarrow> U i: U j" and
+  in_Uj_if_in_Ui: "A: U i \<Longrightarrow> i < j \<Longrightarrow> A: U j"
 
-lemma U_in_U:
+lemma Ui_in_USi:
   "U i: U (S i)"
-  by (rule U_hierarchy, rule lt_S)
+  by (rule Ui_in_Uj, rule lt_S)
 
-lemma lift_U:
+lemma in_USi_if_in_Ui:
   "A: U i \<Longrightarrow> A: U (S i)"
-  by (erule U_cumulative, rule lt_S)
+  by (erule in_Uj_if_in_Ui, rule lt_S)
 
 
-section \<open>\<Prod>-type\<close>
+subsection \<open>\<Prod>-type\<close>
 
 axiomatization
   Pi  :: \<open>o \<Rightarrow> (o \<Rightarrow> o) \<Rightarrow> o\<close> and
@@ -100,9 +114,9 @@ translations
 abbreviation Fn (infixr "\<rightarrow>" 40) where "A \<rightarrow> B \<equiv> \<Prod>_: A. B"
 
 axiomatization where
-  PiF: "\<lbrakk>\<And>x. x: A \<Longrightarrow> B x: U i; A: U i\<rbrakk> \<Longrightarrow> \<Prod>x: A. B x: U i" and
+  PiF: "\<lbrakk>A: U i; \<And>x. x: A \<Longrightarrow> B x: U i\<rbrakk> \<Longrightarrow> \<Prod>x: A. B x: U i" and
 
-  PiI: "\<lbrakk>\<And>x. x: A \<Longrightarrow> b x: B x; A: U i\<rbrakk> \<Longrightarrow> \<lambda>x: A. b x: \<Prod>x: A. B x" and
+  PiI: "\<lbrakk>A: U i; \<And>x. x: A \<Longrightarrow> b x: B x\<rbrakk> \<Longrightarrow> \<lambda>x: A. b x: \<Prod>x: A. B x" and
 
   PiE: "\<lbrakk>f: \<Prod>x: A. B x; a: A\<rbrakk> \<Longrightarrow> f `a: B a" and
 
@@ -113,14 +127,14 @@ axiomatization where
   Pi_cong: "\<lbrakk>
     \<And>x. x: A \<Longrightarrow> B x \<equiv> B' x;
     A: U i;
-    \<And>x. x: A \<Longrightarrow> B x: U i;
-    \<And>x. x: A \<Longrightarrow> B' x: U i
+    \<And>x. x: A \<Longrightarrow> B x: U j;
+    \<And>x. x: A \<Longrightarrow> B' x: U j
     \<rbrakk> \<Longrightarrow> \<Prod>x: A. B x \<equiv> \<Prod>x: A. B' x" and
 
   lam_cong: "\<lbrakk>\<And>x. x: A \<Longrightarrow> b x \<equiv> c x; A: U i\<rbrakk> \<Longrightarrow> \<lambda>x: A. b x \<equiv> \<lambda>x: A. c x"
 
 
-section \<open>\<Sum>-type\<close>
+subsection \<open>\<Sum>-type\<close>
 
 axiomatization
   Sig    :: \<open>o \<Rightarrow> (o \<Rightarrow> o) \<Rightarrow> o\<close> and
@@ -138,16 +152,16 @@ abbreviation "and" (infixl "\<and>" 60)
   where "A \<and> B \<equiv> A \<times> B"
 
 axiomatization where
-  SigF: "\<lbrakk>\<And>x. x: A \<Longrightarrow> B x: U i; A: U i\<rbrakk> \<Longrightarrow> \<Sum>x: A. B x: U i" and
+  SigF: "\<lbrakk>A: U i; \<And>x. x: A \<Longrightarrow> B x: U i\<rbrakk> \<Longrightarrow> \<Sum>x: A. B x: U i" and
 
   SigI: "\<lbrakk>\<And>x. x: A \<Longrightarrow> B x: U i; a: A; b: B a\<rbrakk> \<Longrightarrow> <a, b>: \<Sum>x: A. B x" and
 
   SigE: "\<lbrakk>
     p: \<Sum>x: A. B x;
     A: U i;
-    \<And>x. x : A \<Longrightarrow> B x: U i;
-    \<And>x y. \<lbrakk>x: A; y: B x\<rbrakk> \<Longrightarrow> f x y: C <x, y>;
-    \<And>p. p: \<Sum>x: A. B x \<Longrightarrow> C p: U i
+    \<And>x. x : A \<Longrightarrow> B x: U j;
+    \<And>p. p: \<Sum>x: A. B x \<Longrightarrow> C p: U k;
+    \<And>x y. \<lbrakk>x: A; y: B x\<rbrakk> \<Longrightarrow> f x y: C <x, y>
     \<rbrakk> \<Longrightarrow> SigInd A (fn x. B x) (fn p. C p) f p: C p" and
 
   Sig_comp: "\<lbrakk>
@@ -161,22 +175,23 @@ axiomatization where
   Sig_cong: "\<lbrakk>
     \<And>x. x: A \<Longrightarrow> B x \<equiv> B' x;
     A: U i;
-    \<And>x. x : A \<Longrightarrow> B x: U i;
-    \<And>x. x : A \<Longrightarrow> B' x: U i
+    \<And>x. x : A \<Longrightarrow> B x: U j;
+    \<And>x. x : A \<Longrightarrow> B' x: U j
     \<rbrakk> \<Longrightarrow> \<Sum>x: A. B x \<equiv> \<Sum>x: A. B' x"
 
 
 section \<open>Infrastructure\<close>
 
 ML_file \<open>lib.ML\<close>
-ML_file \<open>typechecking.ML\<close>
+ML_file \<open>context_tactical.ML\<close>
 
 subsection \<open>Proof commands\<close>
 
+ML_file \<open>focus.ML\<close>
+
 named_theorems typechk
 
 ML_file \<open>goals.ML\<close>
-ML_file \<open>focus.ML\<close>
 
 subsection \<open>Congruence automation\<close>
 
@@ -184,72 +199,75 @@ consts "rhs" :: \<open>'a\<close> ("..")
 
 ML_file \<open>congruence.ML\<close>
 
+subsection \<open>Proof methods and type-checking/inference\<close>
+
+named_theorems form and intro and intros and comp
+\<comment> \<open>`intros` stores the introduction rule variants used by the
+  `intro` and `intros` methods.\<close>
+
 ML_file \<open>elimination.ML\<close> \<comment> \<open>elimination rules\<close>
 ML_file \<open>cases.ML\<close> \<comment> \<open>case reasoning rules\<close>
 
-subsection \<open>Methods\<close>
-
-named_theorems intros and comps
 lemmas
-  [intros] = PiF PiI SigF SigI and
-  [elims "?f"] = PiE and
-  [elims "?p"] = SigE and
-  [comps] = beta Sig_comp and
+  [form] = PiF SigF and
+  [intro] = PiI SigI and
+  [intros] = PiI[rotated] SigI and
+  [elim "?f"] = PiE and
+  [elim "?p"] = SigE and
+  [comp] = beta Sig_comp and
   [cong] = Pi_cong lam_cong Sig_cong
 
+ML_file \<open>typechecking.ML\<close>
 ML_file \<open>tactics.ML\<close>
 
-method_setup assumptions =
-  \<open>Scan.succeed (fn ctxt => SIMPLE_METHOD (
-    CHANGED (TRYALL (assumptions_tac ctxt))))\<close>
+method_setup typechk =
+  \<open>Scan.succeed (K (CONTEXT_METHOD (
+    CHEADGOAL o Types.check_infer)))\<close>
 
 method_setup known =
-  \<open>Scan.succeed (fn ctxt => SIMPLE_METHOD (
-    CHANGED (TRYALL (known_tac ctxt))))\<close>
+  \<open>Scan.succeed (K (CONTEXT_METHOD (
+    CHEADGOAL o Types.known_ctac)))\<close>
+
+method_setup rule =
+  \<open>Attrib.thms >> (fn ths => K (CONTEXT_METHOD (
+    CHEADGOAL o SIDE_CONDS (rule_ctac ths))))\<close>
+
+method_setup dest =
+  \<open>Scan.lift (Scan.option (Args.parens Parse.int))
+    -- Attrib.thms >> (fn (n_opt, ths) => K (CONTEXT_METHOD (
+      CHEADGOAL o SIDE_CONDS (dest_ctac n_opt ths))))\<close>
 
 method_setup intro =
-  \<open>Scan.succeed (fn ctxt => SIMPLE_METHOD (HEADGOAL (intro_tac ctxt)))\<close>
+  \<open>Scan.succeed (K (CONTEXT_METHOD (
+    CHEADGOAL o SIDE_CONDS (intro_ctac))))\<close>
 
 method_setup intros =
-  \<open>Scan.succeed (fn ctxt => SIMPLE_METHOD (HEADGOAL (intros_tac ctxt)))\<close>
+  \<open>Scan.succeed (K (CONTEXT_METHOD (
+    CHEADGOAL o SIDE_CONDS (CREPEAT o intro_ctac))))\<close>
 
 method_setup elim =
-  \<open>Scan.repeat Args.term >> (fn tms => fn ctxt =>
-    CONTEXT_METHOD (K (elim_context_tac tms ctxt 1)))\<close>
+  \<open>Scan.repeat Args.term >> (fn tms => K (CONTEXT_METHOD (
+    CHEADGOAL o SIDE_CONDS (elim_ctac tms))))\<close>
 
 method elims = elim+
 
 method_setup cases =
-  \<open>Args.term >> (fn tm => fn ctxt => SIMPLE_METHOD' (cases_tac tm ctxt))\<close>
-
-(*This could possibly use additional simplification hints via a simp: modifier*)
-method_setup typechk =
-  \<open>Scan.succeed (fn ctxt => SIMPLE_METHOD' (
-    SIDE_CONDS (typechk_tac ctxt) ctxt))
-    (* CHANGED (ALLGOALS (TRY o typechk_tac ctxt)))) *)\<close>
+  \<open>Args.term >> (fn tm => K (CONTEXT_METHOD (
+    CHEADGOAL o SIDE_CONDS (cases_ctac tm))))\<close>
 
-method_setup rule =
-  \<open>Attrib.thms >> (fn ths => fn ctxt =>
-    SIMPLE_METHOD (HEADGOAL (SIDE_CONDS (rule_tac ths ctxt) ctxt)))\<close>
-
-method_setup dest =
-  \<open>Scan.lift (Scan.option (Args.parens Parse.int)) -- Attrib.thms
-    >> (fn (opt_n, ths) => fn ctxt =>
-        SIMPLE_METHOD (HEADGOAL (SIDE_CONDS (dest_tac opt_n ths ctxt) ctxt)))\<close>
 
 subsection \<open>Reflexivity\<close>
 
 named_theorems refl
 method refl = (rule refl)
 
-subsection \<open>Trivial proofs modulo typechecking\<close>
+subsection \<open>Trivial proofs (modulo automatic discharge of side conditions)\<close>
 
 method_setup this =
-  \<open>Scan.succeed (fn ctxt => METHOD (
-    EVERY o map (HEADGOAL o
-      (fn ths => SIDE_CONDS (resolve_tac ctxt ths) ctxt) o
-      single)
-    ))\<close>
+  \<open>Scan.succeed (K (CONTEXT_METHOD (fn facts =>
+    CHEADGOAL (SIDE_CONDS
+      (CONTEXT_TACTIC' (fn ctxt => resolve_tac ctxt facts))
+      facts))))\<close>
 
 subsection \<open>Rewriting\<close>
 
@@ -270,7 +288,7 @@ lemma eta_expand:
 lemma rewr_imp:
   assumes "PROP A \<equiv> PROP B"
   shows "(PROP A \<Longrightarrow> PROP C) \<equiv> (PROP B \<Longrightarrow> PROP C)"
-  apply (rule Pure.equal_intr_rule)
+  apply (Pure.rule Pure.equal_intr_rule)
   apply (drule equal_elim_rule2[OF assms]; assumption)
   apply (drule equal_elim_rule1[OF assms]; assumption)
   done
@@ -288,9 +306,11 @@ ML_file \<open>~~/src/HOL/Library/cconv.ML\<close>
 ML_file \<open>rewrite.ML\<close>
 
 \<comment> \<open>\<open>reduce\<close> computes terms via judgmental equalities\<close>
-setup \<open>map_theory_simpset (fn ctxt => ctxt addSolver (mk_solver "" typechk_tac))\<close>
+setup \<open>map_theory_simpset (fn ctxt =>
+  ctxt addSolver (mk_solver "" (fn ctxt' =>
+    NO_CONTEXT_TACTIC ctxt' o Types.check_infer (Simplifier.prems_of ctxt'))))\<close>
 
-method reduce uses add = (simp add: comps add | subst comps)+
+method reduce uses add = changed \<open>((simp add: comp add | sub comp); typechk?)+\<close>
 
 subsection \<open>Implicits\<close>
 
@@ -348,13 +368,19 @@ lemma eta_exp:
   shows "f \<equiv> \<lambda>x: A. f x"
   by (rule eta[symmetric])
 
+lemma refine_codomain:
+  assumes
+    "A: U i"
+    "f: \<Prod>x: A. B x"
+    "\<And>x. x: A \<Longrightarrow> f `x: C x"
+  shows "f: \<Prod>x: A. C x"
+  by (subst eta_exp)
+
 lemma lift_universe_codomain:
   assumes "A: U i" "f: A \<rightarrow> U j"
   shows "f: A \<rightarrow> U (S j)"
-  apply (sub eta_exp)
-    apply known
-    apply (Pure.rule intros; rule lift_U)
-  done
+  using in_USi_if_in_Ui[of "f {}"]
+  by (rule refine_codomain)
 
 subsection \<open>Function composition\<close>
 
@@ -376,7 +402,7 @@ lemma funcompI [typechk]:
     "g \<circ>\<^bsub>A\<^esub> f: \<Prod>x: A. C (f x)"
   unfolding funcomp_def by typechk
 
-lemma funcomp_assoc [comps]:
+lemma funcomp_assoc [comp]:
   assumes
     "f: A \<rightarrow> B"
     "g: B \<rightarrow> C"
@@ -386,7 +412,7 @@ lemma funcomp_assoc [comps]:
     "(h \<circ>\<^bsub>B\<^esub> g) \<circ>\<^bsub>A\<^esub> f \<equiv> h \<circ>\<^bsub>A\<^esub> g \<circ>\<^bsub>A\<^esub> f"
   unfolding funcomp_def by reduce
 
-lemma funcomp_lambda_comp [comps]:
+lemma funcomp_lambda_comp [comp]:
   assumes
     "A: U i"
     "\<And>x. x: A \<Longrightarrow> b x: B"
@@ -395,7 +421,7 @@ lemma funcomp_lambda_comp [comps]:
     "(\<lambda>x: B. c x) \<circ>\<^bsub>A\<^esub> (\<lambda>x: A. b x) \<equiv> \<lambda>x: A. c (b x)"
   unfolding funcomp_def by reduce
 
-lemma funcomp_apply_comp [comps]:
+lemma funcomp_apply_comp [comp]:
   assumes
     "f: A \<rightarrow> B" "g: \<Prod>x: B. C x"
     "x: A"
@@ -417,22 +443,22 @@ abbreviation id where "id A \<equiv> \<lambda>x: A. x"
 
 lemma
   id_type[typechk]: "A: U i \<Longrightarrow> id A: A \<rightarrow> A" and
-  id_comp [comps]: "x: A \<Longrightarrow> (id A) x \<equiv> x" \<comment> \<open>for the occasional manual rewrite\<close>
-  by reduce
+  id_comp [comp]: "x: A \<Longrightarrow> (id A) x \<equiv> x" \<comment> \<open>for the occasional manual rewrite\<close>
+  by reduce+
 
-lemma id_left [comps]:
+lemma id_left [comp]:
   assumes "f: A \<rightarrow> B" "A: U i" "B: U i"
   shows "(id B) \<circ>\<^bsub>A\<^esub> f \<equiv> f"
   by (subst eta_exp[of f]) (reduce, rule eta)
 
-lemma id_right [comps]:
+lemma id_right [comp]:
   assumes "f: A \<rightarrow> B" "A: U i" "B: U i"
   shows "f \<circ>\<^bsub>A\<^esub> (id A) \<equiv> f"
   by (subst eta_exp[of f]) (reduce, rule eta)
 
 lemma id_U [typechk]:
   "id (U i): U i \<rightarrow> U i"
-  by typechk (fact U_in_U)
+  by typechk (rule Ui_in_USi) (*FIXME: Add annotation rule to typechecker*)
 
 
 section \<open>Pairs\<close>
@@ -445,7 +471,7 @@ lemma fst_type [typechk]:
   shows "fst A B: (\<Sum>x: A. B x) \<rightarrow> A"
   unfolding fst_def by typechk
 
-lemma fst_comp [comps]:
+lemma fst_comp [comp]:
   assumes
     "a: A"
     "b: B a"
@@ -459,10 +485,10 @@ lemma snd_type [typechk]:
   shows "snd A B: \<Prod>p: \<Sum>x: A. B x. B (fst A B p)"
   unfolding snd_def by typechk reduce
 
-lemma snd_comp [comps]:
+lemma snd_comp [comp]:
   assumes "a: A" "b: B a" "A: U i" "\<And>x. x: A \<Longrightarrow> B x: U i"
   shows "snd A B <a, b> \<equiv> b"
-  unfolding snd_def by reduce
+  unfolding snd_def by reduce+
 
 subsection \<open>Notation\<close>
 
@@ -483,7 +509,7 @@ Lemma fst [typechk]:
     "p: \<Sum>x: A. B x"
     "A: U i" "\<And>x. x: A \<Longrightarrow> B x: U i"
   shows "fst p: A"
-  by typechk
+  by typechk    
 
 Lemma snd [typechk]:
   assumes
diff --git a/spartan/core/context_tactical.ML b/spartan/core/context_tactical.ML
new file mode 100644
index 0000000..a5159f6
--- /dev/null
+++ b/spartan/core/context_tactical.ML
@@ -0,0 +1,152 @@
+(*  Title:      context_tactical.ML
+    Author:     Joshua Chen
+
+More context tactics, and context tactic combinators.
+*)
+
+infix 1 CTHEN CTHEN' CTHEN_ALL_NEW CTHEN_ALL_NEW_FWD
+infix 0 CORELSE CAPPEND CORELSE' CAPPEND'
+
+structure Context_Tactical:
+sig
+
+type context_tactic' = int -> context_tactic
+val CONTEXT_TACTIC': (Proof.context -> int -> tactic) -> context_tactic'
+val all_ctac: context_tactic
+val no_ctac: context_tactic
+val print_ctac: (Proof.context -> string) -> context_tactic
+val CTHEN: context_tactic * context_tactic -> context_tactic
+val CORELSE: context_tactic * context_tactic -> context_tactic
+val CAPPEND: context_tactic * context_tactic -> context_tactic
+val CTHEN': context_tactic' * context_tactic' -> context_tactic'
+val CORELSE': context_tactic' * context_tactic' -> context_tactic'
+val CAPPEND': context_tactic' * context_tactic' -> context_tactic'
+val CTRY: context_tactic -> context_tactic
+val CREPEAT: context_tactic -> context_tactic
+val CFILTER: (context_state -> bool) -> context_tactic -> context_tactic
+val CCHANGED: context_tactic -> context_tactic
+val CTHEN_ALL_NEW: context_tactic' * context_tactic' -> context_tactic'
+val CREPEAT_IN_RANGE: int -> int -> context_tactic' -> context_tactic
+val CREPEAT_ALL_NEW: context_tactic' -> context_tactic'
+val CTHEN_ALL_NEW_FWD: context_tactic' * context_tactic' -> context_tactic'
+val CREPEAT_ALL_NEW_FWD: context_tactic' -> context_tactic'
+val CHEADGOAL: context_tactic' -> context_tactic
+val CALLGOALS: context_tactic' -> context_tactic
+val CSOMEGOAL: context_tactic' -> context_tactic
+val CRANGE: context_tactic' list -> context_tactic'
+
+end = struct
+
+type context_tactic' = int -> context_tactic
+
+fun CONTEXT_TACTIC' tac i (ctxt, st) = TACTIC_CONTEXT ctxt ((tac ctxt i) st)
+
+val all_ctac = Seq.make_results o Seq.single
+val no_ctac = K Seq.empty
+fun print_ctac f (ctxt, st) = CONTEXT_TACTIC (print_tac ctxt (f ctxt)) (ctxt, st)
+
+fun (ctac1 CTHEN ctac2) cst =  Seq.maps_results ctac2 (ctac1 cst)
+
+fun (ctac1 CORELSE ctac2) cst =
+  (case Seq.pull (ctac1 cst) of
+    NONE => ctac2 cst
+  | some => Seq.make (fn () => some))
+
+fun (ctac1 CAPPEND ctac2) cst =
+  Seq.append (ctac1 cst) (Seq.make (fn () => Seq.pull (ctac2 cst)))
+
+fun (ctac1 CTHEN' ctac2) x = ctac1 x CTHEN ctac2 x
+fun (ctac1 CORELSE' ctac2) x = ctac1 x CORELSE ctac2 x
+fun (ctac1 CAPPEND' ctac2) x = ctac1 x CAPPEND ctac2 x
+
+fun CTRY ctac = ctac CORELSE all_ctac
+
+fun CREPEAT ctac =
+  let
+    fun rep qs cst =
+      (case Seq.pull (Seq.filter_results (ctac cst)) of
+        NONE => SOME (cst, Seq.make (fn () => repq qs))
+      | SOME (cst', q) => rep (q :: qs) cst')
+    and repq [] = NONE
+      | repq (q :: qs) =
+          (case Seq.pull q of
+            NONE => repq qs
+          | SOME (cst, q) => rep (q :: qs) cst);
+  in fn cst => Seq.make_results (Seq.make (fn () => rep [] cst)) end
+
+fun CFILTER pred ctac cst =
+  ctac cst
+  |> Seq.filter_results
+  |> Seq.filter pred
+  |> Seq.make_results
+
+(*Only accept next states where the subgoals have changed*)
+fun CCHANGED ctac (cst as (_, st)) =
+  CFILTER (fn (_, st') => not (Thm.eq_thm (st, st'))) ctac cst
+
+local
+  fun op THEN (f, g) x = Seq.maps_results g (f x)
+
+  fun INTERVAL f i j x =
+    if i > j then Seq.make_results (Seq.single x)
+    else op THEN (f j, INTERVAL f i (j - 1)) x
+
+  (*By Peter Lammich: apply tactic to subgoals in interval in a forward manner,
+    skipping over emerging subgoals*)
+  fun INTERVAL_FWD ctac l u (cst as (_, st)) = cst |>
+    (if l > u then all_ctac
+    else (ctac l CTHEN (fn cst' as (_, st') =>
+      let val ofs = Thm.nprems_of st' - Thm.nprems_of st in
+        if ofs < ~1
+        then raise THM (
+          "INTERVAL_FWD: tactic solved more than one goal", ~1, [st, st'])
+        else INTERVAL_FWD ctac (l + 1 + ofs) (u + ofs) cst'
+      end)))
+in
+
+fun (ctac1 CTHEN_ALL_NEW ctac2) i (cst as (_, st)) =
+  cst |> (ctac1 i CTHEN (fn cst' as (_, st') =>
+    INTERVAL ctac2 i (i + Thm.nprems_of st' - Thm.nprems_of st) cst'))
+
+(*By Peter Lammich: apply ctac2 to all subgoals emerging from ctac1, in forward
+  manner*)
+fun (ctac1 CTHEN_ALL_NEW_FWD ctac2) i (cst as (_, st)) =
+  cst |> (ctac1 i CTHEN (fn cst' as (_, st') =>
+    INTERVAL_FWD ctac2 i (i + Thm.nprems_of st' - Thm.nprems_of st) cst'))
+
+(*Repeatedly apply ctac to the i-th until the k-th-from-last subgoals
+  (i.e. leave the last k subgoals alone), until no more changes appear in the
+  goal state.*)
+fun CREPEAT_IN_RANGE i k ctac =
+  let fun interval_ctac (cst as (_, st)) =
+    INTERVAL_FWD ctac i (Thm.nprems_of st - k) cst
+  in CREPEAT (CCHANGED interval_ctac) end
+
+end
+
+fun CREPEAT_ALL_NEW ctac =
+  ctac CTHEN_ALL_NEW (CTRY o (fn i => CREPEAT_ALL_NEW ctac i))
+
+fun CREPEAT_ALL_NEW_FWD ctac =
+  ctac CTHEN_ALL_NEW_FWD (CTRY o (fn i => CREPEAT_ALL_NEW_FWD ctac i))
+
+fun CHEADGOAL ctac = ctac 1
+
+fun CALLGOALS ctac (cst as (_, st)) =
+  let
+    fun doall 0 = all_ctac
+      | doall n = ctac n CTHEN doall (n - 1);
+  in doall (Thm.nprems_of st) cst end
+
+fun CSOMEGOAL ctac (cst as (_, st)) =
+  let
+    fun find 0 = no_ctac
+      | find n = ctac n CORELSE find (n - 1);
+  in find (Thm.nprems_of st) cst end
+
+fun CRANGE [] _ = all_ctac
+  | CRANGE (ctac :: ctacs) i = CRANGE ctacs (i + 1) CTHEN ctac i
+
+end
+
+open Context_Tactical
diff --git a/spartan/core/elimination.ML b/spartan/core/elimination.ML
index 11b3af9..cd4e414 100644
--- a/spartan/core/elimination.ML
+++ b/spartan/core/elimination.ML
@@ -34,13 +34,13 @@ fun register_rule tms rl =
   in Rules.map (Termtab.update (hd, (rl, map (#1 o dest_Var) tms))) end
 
 
-(* [elims] attribute *)
+(* [elim] attribute *)
 val _ = Theory.setup (
-  Attrib.setup \<^binding>\<open>elims\<close>
+  Attrib.setup \<^binding>\<open>elim\<close>
     (Scan.repeat Args.term_pattern >>
       (Thm.declaration_attribute o register_rule))
     ""
-  #> Global_Theory.add_thms_dynamic (\<^binding>\<open>elims\<close>,
+  #> Global_Theory.add_thms_dynamic (\<^binding>\<open>elim\<close>,
       fn context => (map #1 (rules (Context.proof_of context))))
 )
 
diff --git a/spartan/core/eqsubst.ML b/spartan/core/eqsubst.ML
index ea6f098..e7ecf63 100644
--- a/spartan/core/eqsubst.ML
+++ b/spartan/core/eqsubst.ML
@@ -416,19 +416,27 @@ fun eqsubst_asm_tac ctxt occs thms i st =
    should be done to an assumption, false = apply to the conclusion of
    the goal) as well as the theorems to use *)
 val _ =
-  Theory.setup
-    (Method.setup \<^binding>\<open>sub\<close>
-      (Scan.lift (Args.mode "asm" -- Scan.optional (Args.parens (Scan.repeat Parse.nat)) [0]) --
-        Attrib.thms >> (fn ((asm, occs), inthms) => fn ctxt =>
-          SIMPLE_METHOD' ((if asm then eqsubst_asm_tac else eqsubst_tac) ctxt occs inthms)))
-      "single-step substitution"
-    #>
-    (Method.setup \<^binding>\<open>subst\<close>
-      (Scan.lift (Args.mode "asm" -- Scan.optional (Args.parens (Scan.repeat Parse.nat)) [0]) --
-        Attrib.thms >> (fn ((asm, occs), inthms) => fn ctxt =>
-          SIMPLE_METHOD' (SIDE_CONDS
-            ((if asm then eqsubst_asm_tac else eqsubst_tac) ctxt occs inthms)
-            ctxt)))
-      "single-step substitution with auto-typechecking"))
+  let
+    val parser =
+      Scan.lift (Args.mode "asm"
+        -- Scan.optional (Args.parens (Scan.repeat Parse.nat)) [0])
+      -- Attrib.thms
+    fun eqsubst_asm_ctac occs inthms =
+      CONTEXT_TACTIC' (fn ctxt => eqsubst_asm_tac ctxt occs inthms)
+    fun eqsubst_ctac occs inthms =
+      CONTEXT_TACTIC' (fn ctxt => eqsubst_tac ctxt occs inthms)
+  in
+    Theory.setup (
+      Method.setup \<^binding>\<open>sub\<close>
+        (parser >> (fn ((asm, occs), inthms) => fn ctxt => SIMPLE_METHOD' (
+          (if asm then eqsubst_asm_tac else eqsubst_tac) ctxt occs inthms)))
+        "single-step substitution" #>
+      Method.setup \<^binding>\<open>subst\<close>
+        (parser >> (fn ((asm, occs), inthms) => K (CONTEXT_METHOD (
+          CHEADGOAL o SIDE_CONDS
+            ((if asm then eqsubst_asm_ctac else eqsubst_ctac) occs inthms)))))
+        "single-step substitution with automatic discharge of side conditions"
+    )
+  end
 
 end;
diff --git a/spartan/core/lib.ML b/spartan/core/lib.ML
index 615f601..7b93a08 100644
--- a/spartan/core/lib.ML
+++ b/spartan/core/lib.ML
@@ -7,6 +7,7 @@ val maxint: int list -> int
 
 (*Terms*)
 val is_rigid: term -> bool
+val no_vars: term -> bool
 val dest_eq: term -> term * term
 val mk_Var: string -> int -> typ -> term
 val lambda_var: term -> term -> term
@@ -50,6 +51,8 @@ val maxint = max (op >)
 
 val is_rigid = not o is_Var o head_of
 
+val no_vars = not o exists_subterm is_Var
+
 fun dest_eq (Const (\<^const_name>\<open>Pure.eq\<close>, _) $ t $ def) = (t, def)
   | dest_eq _ = error "dest_eq"
 
diff --git a/spartan/core/rewrite.ML b/spartan/core/rewrite.ML
index f9c5d8e..eba0e81 100644
--- a/spartan/core/rewrite.ML
+++ b/spartan/core/rewrite.ML
@@ -15,8 +15,8 @@ patterns but has diverged significantly during its development.
 We also allow introduction of identifiers for bound variables,
 which can then be used to match arbitrary subterms inside abstractions.
 
-This code is slightly modified from the original at HOL/Library/rewrite.ML,
-to incorporate auto-typechecking for type theory.
+This code has been slightly modified from the original at HOL/Library/rewrite.ML
+to incorporate automatic discharge of type-theoretic side conditions.
 *)
 
 infix 1 then_pconv;
@@ -448,18 +448,18 @@ val _ =
     val subst_parser =
       let val scan = raw_pattern -- to_parser -- Parse.thms1
       in context_lift scan prep_args end
+
+    fun rewrite_export_ctac inputs inthms =
+      CONTEXT_TACTIC' (fn ctxt => rewrite_export_tac ctxt inputs inthms)
   in
     Method.setup \<^binding>\<open>rewr\<close> (subst_parser >>
-      (fn (pattern, inthms, (to, pat_ctxt)) => fn orig_ctxt =>
-        SIMPLE_METHOD'
-          (rewrite_export_tac orig_ctxt ((pattern, to), SOME pat_ctxt) inthms)))
-      "single-step rewriting, allowing subterm selection via patterns"
-    #>
-    (Method.setup \<^binding>\<open>rewrite\<close> (subst_parser >>
-      (fn (pattern, inthms, (to, pat_ctxt)) => fn orig_ctxt =>
-        SIMPLE_METHOD' (SIDE_CONDS
-          (rewrite_export_tac orig_ctxt ((pattern, to), SOME pat_ctxt) inthms)
-          orig_ctxt)))
-      "single-step rewriting with auto-typechecking")
+      (fn (pattern, inthms, (to, pat_ctxt)) => fn orig_ctxt => SIMPLE_METHOD'
+        (rewrite_export_tac orig_ctxt ((pattern, to), SOME pat_ctxt) inthms)))
+      "single-step rewriting, allowing subterm selection via patterns" #>
+    Method.setup \<^binding>\<open>rewrite\<close> (subst_parser >>
+      (fn (pattern, inthms, (to, pat_ctxt)) => K (CONTEXT_METHOD (
+        CHEADGOAL o SIDE_CONDS
+          (rewrite_export_ctac ((pattern, to), SOME pat_ctxt) inthms)))))
+      "single-step rewriting with auto-typechecking"
   end
 end
diff --git a/spartan/core/tactics.ML b/spartan/core/tactics.ML
index 0c71665..3922ae0 100644
--- a/spartan/core/tactics.ML
+++ b/spartan/core/tactics.ML
@@ -7,109 +7,66 @@ General tactics for dependent type theory.
 structure Tactics:
 sig
 
-val assumptions_tac: Proof.context -> int -> tactic
-val known_tac: Proof.context -> int -> tactic
-val typechk_tac: Proof.context -> int -> tactic
-val auto_typechk: bool Config.T
-val SIDE_CONDS: (int -> tactic) -> Proof.context -> int -> tactic
-val rule_tac: thm list -> Proof.context -> int -> tactic
-val dest_tac: int option -> thm list -> Proof.context -> int -> tactic
-val intro_tac: Proof.context -> int -> tactic
-val intros_tac: Proof.context -> int -> tactic
-val elim_context_tac: term list -> Proof.context -> int -> context_tactic
-val cases_tac: term -> Proof.context -> int -> tactic
+val solve_side_conds: int Config.T
+val SIDE_CONDS: context_tactic' -> thm list -> context_tactic'
+val rule_ctac: thm list -> context_tactic'
+val dest_ctac: int option -> thm list -> context_tactic'
+val intro_ctac: context_tactic'
+val elim_ctac: term list -> context_tactic'
+val cases_ctac: term -> context_tactic'
 
 end = struct
 
-(*An assumption tactic that only solves typing goals with rigid terms and
-  judgmental equalities without schematic variables*)
-fun assumptions_tac ctxt = SUBGOAL (fn (goal, i) =>
-  let
-    val concl = Logic.strip_assums_concl goal
-  in
-    if
-      Lib.is_typing concl andalso Lib.is_rigid (Lib.term_of_typing concl)
-      orelse not ((exists_subterm is_Var) concl)
-    then assume_tac ctxt i
-    else no_tac
-  end)
-
-(*Solves typing goals with rigid term by resolving with context facts and
-  simplifier premises, or arbitrary goals by *non-unifying* assumption*)
-fun known_tac ctxt = SUBGOAL (fn (goal, i) =>
-  let
-    val concl = Logic.strip_assums_concl goal
-  in
-    ((if Lib.is_typing concl andalso Lib.is_rigid (Lib.term_of_typing concl)
-      then
-        let val ths = map fst (Facts.props (Proof_Context.facts_of ctxt))
-        in resolve_tac ctxt (ths @ Simplifier.prems_of ctxt) end
-      else K no_tac)
-    ORELSE' assumptions_tac ctxt) i
-  end)
-
-(*Typechecking: try to solve goals of the form "a: A" where a is rigid*)
-fun typechk_tac ctxt =
-  let
-    val tac = SUBGOAL (fn (goal, i) =>
-      if Lib.rigid_typing_concl goal
-      then
-        let val net = Tactic.build_net
-          ((Named_Theorems.get ctxt \<^named_theorems>\<open>typechk\<close>)
-          @(Named_Theorems.get ctxt \<^named_theorems>\<open>intros\<close>)
-          @(map #1 (Elim.rules ctxt)))
-        in (resolve_from_net_tac ctxt net) i end
-      else no_tac)
-  in
-    REPEAT_ALL_NEW (known_tac ctxt ORELSE' tac)
-  end
 
-fun typechk_context_tac (ctxt, st) =
-  let
-    
-  in
-    ()
-  end
+(* Side conditions *)
+val solve_side_conds =
+  Attrib.setup_config_int \<^binding>\<open>solve_side_conds\<close> (K 2)
 
-(*Many methods try to automatically discharge side conditions by typechecking.
-  Switch this flag off to discharge by non-unifying assumption instead.*)
-val auto_typechk = Attrib.setup_config_bool \<^binding>\<open>auto_typechk\<close> (K true)
+fun SIDE_CONDS ctac facts i (cst as (ctxt, st)) = cst |> (ctac i CTHEN
+  (case Config.get ctxt solve_side_conds of
+    1 => CALLGOALS (CTRY o Types.known_ctac facts)
+  | 2 => CREPEAT_IN_RANGE i (Thm.nprems_of st - i)
+      (CTRY o CREPEAT_ALL_NEW_FWD (Types.check_infer facts))
+  | _ => all_ctac))
 
-fun side_cond_tac ctxt = CHANGED o REPEAT o
-  (if Config.get ctxt auto_typechk then typechk_tac ctxt else known_tac ctxt)
 
-(*Combinator runs tactic and tries to discharge all new typing side conditions*)
-fun SIDE_CONDS tac ctxt = tac THEN_ALL_NEW (TRY o side_cond_tac ctxt)
+(* rule, dest, intro *)
 
 local
-fun mk_rules _ ths [] = ths
-  | mk_rules n ths ths' =
-      let val ths'' = foldr1 (op @)
-        (map (fn th => [rotate_prems n (th RS @{thm PiE})] handle THM _ => []) ths')
-      in
-        mk_rules n (ths @ ths') ths''
-      end
+  fun mk_rules _ ths [] = ths
+    | mk_rules n ths ths' =
+        let val ths'' = foldr1 (op @)
+          (map
+            (fn th => [rotate_prems n (th RS @{thm PiE})] handle THM _ => [])
+            ths')
+        in
+          mk_rules n (ths @ ths') ths''
+        end
 in
 
-(*Resolves with given rules, discharging as many side conditions as possible*)
-fun rule_tac ths ctxt = resolve_tac ctxt (mk_rules 0 [] ths)
+(*Resolves with given rules*)
+fun rule_ctac ths i (ctxt, st) =
+  TACTIC_CONTEXT ctxt (resolve_tac ctxt (mk_rules 0 [] ths) i st)
 
 (*Attempts destruct-resolution with the n-th premise of the given rules*)
-fun dest_tac opt_n ths ctxt = dresolve_tac ctxt
-  (mk_rules (case opt_n of NONE => 0 | SOME 0 => 0 | SOME n => n-1) [] ths)
+fun dest_ctac opt_n ths i (ctxt, st) =
+  TACTIC_CONTEXT ctxt (dresolve_tac ctxt
+    (mk_rules (case opt_n of NONE => 0 | SOME 0 => 0 | SOME n => n-1) [] ths)
+    i st)
 
 end
 
 (*Applies some introduction rule*)
-fun intro_tac ctxt = SUBGOAL (fn (_, i) => SIDE_CONDS
-  (resolve_tac ctxt (Named_Theorems.get ctxt \<^named_theorems>\<open>intros\<close>)) ctxt i)
+fun intro_ctac i (ctxt, st) = TACTIC_CONTEXT ctxt (resolve_tac ctxt
+  (Named_Theorems.get ctxt \<^named_theorems>\<open>intros\<close>) i st)
 
-fun intros_tac ctxt = SUBGOAL (fn (_, i) =>
-  (CHANGED o REPEAT o CHANGED o intro_tac ctxt) i)
 
 (* Induction/elimination *)
 
-(*Pushes a context/goal premise typing t:T into a \<Prod>-type*)
+(*Pushes a known typing t:T into a \<Prod>-type.
+  This tactic is well-behaved only when t is sufficiently well specified
+  (otherwise there might be multiple possible judgments t:T that unify, and
+  which is chosen is undefined).*)
 fun internalize_fact_tac t =
   Subgoal.FOCUS_PARAMS (fn {context = ctxt, concl = raw_concl, ...} =>
     let
@@ -123,18 +80,10 @@ fun internalize_fact_tac t =
     in
       HEADGOAL (resolve_tac ctxt [resolvent])
       (*known_tac infers the correct type T inferred by unification*)
-      THEN SOMEGOAL (known_tac ctxt)
+      THEN SOMEGOAL (NO_CONTEXT_TACTIC ctxt o Types.known_ctac [])
     end)
 
-(*Premises that have already been pushed into the \<Prod>-type*)
-structure Inserts = Proof_Data (
-  type T = term Item_Net.T
-  val init = K (Item_Net.init Term.aconv_untyped single)
-)
-
-local
-
-fun elim_core_tac tms types ctxt = SUBGOAL (K (
+fun elim_core_tac tms types ctxt =
   let
     val rule_insts = map ((Elim.lookup_rule ctxt) o Term.head_of) types
     val rules = flat (map
@@ -144,84 +93,86 @@ fun elim_core_tac tms types ctxt = SUBGOAL (K (
           (idxnames ~~ map (Thm.cterm_of ctxt) tms) rl])
       rule_insts)
   in
-    HEADGOAL (resolve_tac ctxt rules)
-    THEN RANGE (replicate (length tms) (typechk_tac ctxt)) 1
-  end handle Option => no_tac))
+    resolve_tac ctxt rules
+    THEN' RANGE (replicate (length tms) (NO_CONTEXT_TACTIC ctxt o Types.check_infer []))
+  end handle Option => K no_tac
 
-in
-
-fun elim_context_tac tms ctxt = case tms of
-    [] => CONTEXT_SUBGOAL (K (Context_Tactic.CONTEXT_TACTIC (HEADGOAL (
-      SIDE_CONDS (eresolve_tac ctxt (map #1 (Elim.rules ctxt))) ctxt))))
-  | major::_  => CONTEXT_SUBGOAL (fn (goal, _) =>
-    let
-      val facts = Proof_Context.facts_of ctxt
-      val prems = Logic.strip_assums_hyp goal
-      val template = Lib.typing_of_term major
-      val types =
-        map (Thm.prop_of o #1) (Facts.could_unify facts template)
-        @ filter (fn prem => Term.could_unify (template, prem)) prems
-        |> map Lib.type_of_typing
-    in case types of
-        [] => Context_Tactic.CONTEXT_TACTIC no_tac
-      | _ =>
-        let
-          val inserts = map (Thm.prop_of o fst) (Facts.props facts) @ prems
-            |> filter Lib.is_typing
-            |> map Lib.dest_typing
-            |> filter_out (fn (t, _) =>
-              Term.aconv (t, major) orelse Item_Net.member (Inserts.get ctxt) t)
-            |> map (fn (t, T) => ((t, T), Lib.subterm_count_distinct tms T))
-            |> filter (fn (_, i) => i > 0)
-            (*`t1: T1` comes before `t2: T2` if T1 contains t2 as subterm.
-              If they are incomparable, then order by decreasing
-              `subterm_count [p, x, y] T`*)
-            |> sort (fn (((t1, _), i), ((_, T2), j)) =>
-                Lib.cond_order (Lib.subterm_order T2 t1) (int_ord (j, i)))
-            |> map (#1 o #1)
-          val record_inserts = Inserts.map (fold Item_Net.update inserts)
-          val tac =
-            (*Push premises having a subterm in `tms` into a \<Prod>*)
-            fold (fn t => fn tac =>
-              tac THEN HEADGOAL (internalize_fact_tac t ctxt))
-              inserts all_tac
-            (*Apply elimination rule*)
-            THEN (HEADGOAL (
-              elim_core_tac tms types ctxt
-              (*Pull pushed premises back out*)
-              THEN_ALL_NEW (SUBGOAL (fn (_, i) =>
-                REPEAT_DETERM_N (length inserts)
-                  (resolve_tac ctxt @{thms PiI} i)))
-            ))
-            (*Side conditions*)
-            THEN ALLGOALS (TRY o side_cond_tac ctxt)
-        in
-          fn (ctxt, st) => Context_Tactic.TACTIC_CONTEXT
-            (record_inserts ctxt) (tac st)
-        end
-    end)
+(*Premises that have already been pushed into the \<Prod>-type*)
+structure Inserts = Proof_Data (
+  type T = term Item_Net.T
+  val init = K (Item_Net.init Term.aconv_untyped single)
+)
 
-fun cases_tac tm ctxt = SUBGOAL (fn (goal, i) =>
-  let
-    val facts = Proof_Context.facts_of ctxt
-    val prems = Logic.strip_assums_hyp goal
-    val template = Lib.typing_of_term tm
-    val types =
-      map (Thm.prop_of o #1) (Facts.could_unify facts template)
-      @ filter (fn prem => Term.could_unify (template, prem)) prems
-      |> map Lib.type_of_typing
-    val res = (case types of
-        [typ] => Drule.infer_instantiate' ctxt [SOME (Thm.cterm_of ctxt tm)]
-          (the (Case.lookup_rule ctxt (Term.head_of typ)))
-      | [] => raise Option
-      | _ => raise error (Syntax.string_of_term ctxt tm ^ "not uniquely typed"))
-      handle Option => error ("no case rule known for "
-        ^ (Syntax.string_of_term ctxt tm))
-  in
-    SIDE_CONDS (resolve_tac ctxt [res]) ctxt i
-  end)
+fun elim_ctac tms =
+  case tms of
+    [] => CONTEXT_TACTIC' (fn ctxt => eresolve_tac ctxt (map #1 (Elim.rules ctxt)))
+  | major :: _ => CONTEXT_SUBGOAL (fn (goal, _) => fn cst as (ctxt, st) =>
+      let
+        val facts = Proof_Context.facts_of ctxt
+        val prems = Logic.strip_assums_hyp goal
+        val template = Lib.typing_of_term major
+        val types =
+          map (Thm.prop_of o #1) (Facts.could_unify facts template)
+          @ filter (fn prem => Term.could_unify (template, prem)) prems
+          |> map Lib.type_of_typing
+      in case types of
+          [] => no_ctac cst
+        | _ =>
+            let
+              val inserts = map (Thm.prop_of o fst) (Facts.props facts) @ prems
+                |> filter Lib.is_typing
+                |> map Lib.dest_typing
+                |> filter_out (fn (t, _) =>
+                  Term.aconv (t, major) orelse Item_Net.member (Inserts.get ctxt) t)
+                |> map (fn (t, T) => ((t, T), Lib.subterm_count_distinct tms T))
+                |> filter (fn (_, i) => i > 0)
+                (*`t1: T1` comes before `t2: T2` if T1 contains t2 as subterm.
+                  If they are incomparable, then order by decreasing
+                  `subterm_count [p, x, y] T`*)
+                |> sort (fn (((t1, _), i), ((_, T2), j)) =>
+                    Lib.cond_order (Lib.subterm_order T2 t1) (int_ord (j, i)))
+                |> map (#1 o #1)
+              val record_inserts = Inserts.map (fold Item_Net.update inserts)
+              val tac =
+                (*Push premises having a subterm in `tms` into a \<Prod>*)
+                fold (fn t => fn tac =>
+                  tac THEN HEADGOAL (internalize_fact_tac t ctxt))
+                  inserts all_tac
+                (*Apply elimination rule*)
+                THEN HEADGOAL (
+                  elim_core_tac tms types ctxt
+                  (*Pull pushed premises back out*)
+                  THEN_ALL_NEW (SUBGOAL (fn (_, i) =>
+                    REPEAT_DETERM_N (length inserts)
+                      (resolve_tac ctxt @{thms PiI[rotated]} i))))
+            in
+              TACTIC_CONTEXT (record_inserts ctxt) (tac st)
+            end
+      end)
+
+fun cases_ctac tm =
+  let fun tac ctxt =
+    SUBGOAL (fn (goal, i) =>
+      let
+        val facts = Proof_Context.facts_of ctxt
+        val prems = Logic.strip_assums_hyp goal
+        val template = Lib.typing_of_term tm
+        val types =
+          map (Thm.prop_of o #1) (Facts.could_unify facts template)
+          @ filter (fn prem => Term.could_unify (template, prem)) prems
+          |> map Lib.type_of_typing
+        val res = (case types of
+            [typ] => Drule.infer_instantiate' ctxt [SOME (Thm.cterm_of ctxt tm)]
+              (the (Case.lookup_rule ctxt (Term.head_of typ)))
+          | [] => raise Option
+          | _ => raise error (Syntax.string_of_term ctxt tm ^ "not uniquely typed"))
+          handle Option =>
+            error ("no case rule known for " ^ (Syntax.string_of_term ctxt tm))
+      in
+        resolve_tac ctxt [res] i
+      end)
+  in CONTEXT_TACTIC' tac end
 
-end
 
 end
 
diff --git a/spartan/core/typechecking.ML b/spartan/core/typechecking.ML
index 437a2dc..946ecd6 100644
--- a/spartan/core/typechecking.ML
+++ b/spartan/core/typechecking.ML
@@ -1,7 +1,7 @@
 (*  Title:      typechecking.ML
     Author:     Joshua Chen
 
-Type information and typechecking infrastructure.
+Type information and type-checking infrastructure.
 *)
 
 structure Types: sig
@@ -11,11 +11,12 @@ val types: Proof.context -> term -> thm list
 val put_type: thm -> Proof.context -> Proof.context
 val put_types: thm list -> Proof.context -> Proof.context
 
-val check: Proof.context -> thm -> int -> tactic
-val infer: Proof.context -> thm -> int -> tactic
+val known_ctac: thm list -> int -> context_tactic
+val check_infer: thm list -> int -> context_tactic
 
 end = struct
 
+
 (* Context data *)
 
 structure Data = Generic_Data (
@@ -32,22 +33,55 @@ fun put_type typing = Context.proof_map (Data.map (Item_Net.update typing))
 fun put_types typings = foldr1 (op o) (map put_type typings)
 
 
-(* Checking and inference *)
-
+(* Context tactics for type-checking *)
+
+(*Solves goals without metavariables and type inference problems by resolving
+  with facts or assumption from inline premises.*)
+fun known_ctac facts = CONTEXT_SUBGOAL (fn (goal, i) => fn (ctxt, st) =>
+  TACTIC_CONTEXT ctxt
+    let val concl = Logic.strip_assums_concl goal in
+      if Lib.no_vars concl orelse
+        (Lib.is_typing concl andalso Lib.no_vars (Lib.term_of_typing concl))
+      then
+        let val ths = facts
+          (*FIXME: Shouldn't pull nameless facts directly from context*)
+          @ map fst (Facts.props (Proof_Context.facts_of ctxt))
+        in (resolve_tac ctxt ths i ORELSE assume_tac ctxt i) st end
+      else Seq.empty
+    end)
+
+(*Simple bidirectional typing tactic, with some nondeterminism from backtracking
+  search over arbitrary `typechk` rules. The current implementation does not
+  perform any normalization.*)
 local
-
-fun checkable prop = Lib.is_typing prop
-  andalso not (exists_subterm is_Var (Lib.type_of_typing prop))
-
+  fun check_infer_step facts i (ctxt, st) =
+    let
+      val tac = SUBGOAL (fn (goal, i) =>
+        if Lib.rigid_typing_concl goal
+        then
+          let val net = Tactic.build_net (facts
+            (*MAYBE FIXME: Remove `typechk` from this list, and instead perform
+              definitional unfolding to (w?)hnf.*)
+            @(Named_Theorems.get ctxt \<^named_theorems>\<open>typechk\<close>)
+            @(Named_Theorems.get ctxt \<^named_theorems>\<open>form\<close>)
+            @(Named_Theorems.get ctxt \<^named_theorems>\<open>intro\<close>)
+            @(map #1 (Elim.rules ctxt)))
+          in (resolve_from_net_tac ctxt net) i end
+        else no_tac)
+      val ctxt' = ctxt
+    in
+      TACTIC_CONTEXT ctxt' (tac i st)
+    end
 in
 
-fun check ctxt rule = Subgoal.FOCUS_PREMS (
-  fn {context = goal_ctxt, prems, concl, ...} => no_tac) ctxt
-
-fun infer ctxt rule = Subgoal.FOCUS_PREMS (
-  fn {context = goal_ctxt, prems, concl, ...} => no_tac) ctxt
+fun check_infer facts i (cst as (_, st)) =
+  let
+    val ctac = known_ctac facts CORELSE' check_infer_step facts
+  in
+    cst |> (ctac i CTHEN
+      CREPEAT_IN_RANGE i (Thm.nprems_of st - i) (CTRY o CREPEAT_ALL_NEW_FWD ctac))
+  end
 
 end
 
-
 end