SubsetTypes

2024-11-27 23:06:20 +00:00 · 2017-03-21 19:27:36 -04:00 · 2017-03-21 19:27:36 -04:00 · c5600db874
commit c5600db874
parent 88df5601f5
9 changed files with 1038 additions and 390 deletions
--- a/Frap.v
+++ b/Frap.v
@ -1,373 +1,3 @@
-Require Import Eqdep String Arith Omega Program Sets Relations Map Var Invariant Bool ModelCheck.
+Require Export FrapWithoutSets.
 Export String Arith Sets Relations Map Var Invariant Bool ModelCheck.
 Require Import List.
 Export List ListNotations.
 Open Scope string_scope.
 Open Scope list_scope.
-Ltac inductN n :=
+Module Export SN := SetNotations(FrapWithoutSets).
  match goal with
    | [ |- forall x : ?E, _ ] =>
      match type of E with
        | Prop =>
          let H := fresh in intro H;
            match n with
              | 1 => dependent induction H
              | S ?n' => inductN n'
            end
        | _ => intro; inductN n
      end
  end.
 Ltac same_structure x y :=
  match x with
  | ?f ?a1 ?b1 ?c1 ?d1 =>
    match y with
    | f ?a2 ?b2 ?c2 ?d2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2; same_structure d1 d2
    | _ => fail 2
    end
  | ?f ?a1 ?b1 ?c1 =>
    match y with
    | f ?a2 ?b2 ?c2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2
    | _ => fail 2
    end
  | ?f ?a1 ?b1 =>
    match y with
    | f ?a2 ?b2 => same_structure a1 a2; same_structure b1 b2
    | _ => fail 2
    end
  | ?f ?a1 =>
    match y with
    | f ?a2 => same_structure a1 a2
    | _ => fail 2
    end
  | _ =>
    match y with
    | ?f ?a1 ?b1 ?c1 ?d1 =>
      match x with
      | f ?a2 ?b2 ?c2 ?d2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2; same_structure d1 d2
      | _ => fail 2
      end
    | ?f ?a1 ?b1 ?c1 =>
      match x with
      | f ?a2 ?b2 ?c2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2
      | _ => fail 2
      end
    | ?f ?a1 ?b1 =>
      match x with
      | f ?a2 ?b2 => same_structure a1 a2; same_structure b1 b2
      | _ => fail 2
      end
    | ?f ?a1 =>
      match x with
      | f ?a2 => same_structure a1 a2
      | _ => fail 2
      end
    | _ => idtac
    end
  end.
 Ltac instantiate_obvious1 H :=
  match type of H with
  | _ ++ _ = _ ++ _ -> _ => fail 1
  | ?x = ?y -> _ =>
    (same_structure x y; specialize (H eq_refl))
    || (has_evar (x, y); fail 3)
  | JMeq.JMeq ?x ?y -> _ =>
    (same_structure x y; specialize (H JMeq.JMeq_refl))
    || (has_evar (x, y); fail 3)
  | forall x : ?T, _ =>
    match type of T with
    | Prop => fail 1
    | _ =>
      let x' := fresh x in
      evar (x' : T);
      let x'' := eval unfold x' in x' in specialize (H x''); clear x';
        instantiate_obvious1 H
    end
  end.
 Ltac instantiate_obvious H :=
  match type of H with
    | context[@eq string _  _] => idtac
    | _ => repeat instantiate_obvious1 H
  end.
 Ltac instantiate_obviouses :=
  repeat match goal with
         | [ H : _ |- _ ] => instantiate_obvious H
         end.
 Ltac induct e := (inductN e || dependent induction e); instantiate_obviouses.
 Ltac invert' H := inversion H; clear H; subst.
 Ltac invertN n :=
  match goal with
    | [ |- forall x : ?E, _ ] =>
      match type of E with
        | Prop =>
          let H := fresh in intro H;
            match n with
              | 1 => invert' H
              | S ?n' => invertN n'
            end
        | _ => intro; invertN n
      end
  end.
 Ltac invert e := invertN e || invert' e.
 Ltac invert0 e := invert e; fail.
 Ltac invert1 e := invert0 e || (invert e; []).
 Ltac invert2 e := invert1 e || (invert e; [|]).
 Ltac maps_neq :=
  match goal with
  | [ H : ?m1 = ?m2 |- _ ] =>
    let rec recur E :=
        match E with
        | ?E' $+ (?k, _) => 
          (apply (f_equal (fun m => m $? k)) in H; simpl in *; autorewrite with core in *; simpl in *; congruence)
          || recur E'
        end in
    recur m1 || recur m2
 end.
 Ltac fancy_neq :=
  repeat match goal with
         | _ => maps_neq
         | [ H : @eq (nat -> _) _ _ |- _ ] => apply (f_equal (fun f => f 0)) in H
         | [ H : @eq ?T _ _ |- _ ] =>
           match eval compute in T with
           | fmap _ _ => fail 1
           | _ => invert H
           end
         end.
 Ltac maps_equal' := progress Frap.Map.M.maps_equal; autorewrite with core; simpl.
 Ltac removeDups :=
  match goal with
  | [ |- context[constant ?ls] ] =>
    someMatch ls;
    erewrite (@removeDups_ok _ ls)
      by repeat (apply RdNil
                 || (apply RdNew; [ simpl; intuition (congruence || solve [ fancy_neq ]) | ])
                 || (apply RdDup; [ simpl; intuition (congruence || (repeat (maps_equal' || f_equal))) | ]))
  end.
 Ltac doSubtract :=
  match goal with
  | [ |- context[constant ?ls \setminus constant ?ls0] ] =>
    erewrite (@doSubtract_ok _ ls ls0)
      by repeat (apply DsNil
                 || (apply DsKeep; [ simpl; intuition (congruence || solve [ fancy_neq ]) | ])
                 || (apply DsDrop; [ simpl; intuition (congruence || (repeat (maps_equal' || f_equal))) | ]))
  end.
 Ltac simpl_maps :=
  repeat match goal with
         | [ |- context[add ?m ?k1 ?v $? ?k2] ] =>
           (rewrite (@lookup_add_ne _ _ m k1 k2 v) by (congruence || omega))
           || (rewrite (@lookup_add_eq _ _ m k1 k2 v) by (congruence || omega))
         end.
 Ltac simplify := repeat (unifyTails; pose proof I);
                repeat match goal with
                       | [ H : True |- _ ] => clear H
                       end;
                repeat progress (simpl in *; intros; try autorewrite with core in *; simpl_maps);
                                 repeat (normalize_set || doSubtract).
 Ltac propositional := intuition idtac.
 Ltac linear_arithmetic := intros;
    repeat match goal with
           | [ |- context[max ?a ?b] ] =>
             let Heq := fresh "Heq" in destruct (Max.max_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           | [ _ : context[max ?a ?b] |- _ ] =>
             let Heq := fresh "Heq" in destruct (Max.max_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           | [ |- context[min ?a ?b] ] =>
             let Heq := fresh "Heq" in destruct (Min.min_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           | [ _ : context[min ?a ?b] |- _ ] =>
             let Heq := fresh "Heq" in destruct (Min.min_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           end; omega.
 Ltac equality := intuition congruence.
 Ltac cases E :=
  ((is_var E; destruct E)
   || match type of E with
      | {_} + {_} => destruct E
      | _ => let Heq := fresh "Heq" in destruct E eqn:Heq
      end);
  repeat match goal with
         | [ H : _ = left _ |- _ ] => clear H
         | [ H : _ = right _ |- _ ] => clear H
         end.
 Global Opaque max min.
 Infix "==n" := eq_nat_dec (no associativity, at level 50).
 Infix "<=?" := le_lt_dec.
 Export Frap.Map.
 Ltac maps_equal := Frap.Map.M.maps_equal; simplify.
 Ltac first_order := firstorder idtac.
 (** * Model checking *)
 Lemma eq_iff : forall P Q,
    P = Q
    -> (P <-> Q).
 Proof.
  equality.
 Qed.
 Ltac sets0 := Sets.sets ltac:(simpl in *; intuition (subst; auto; try equality; try linear_arithmetic)).
 Ltac sets := propositional;
  try match goal with
      | [ |- @eq (set _) _ _ ] =>
        let x := fresh "x" in
        apply sets_equal; intro x;
        repeat match goal with
               | [ H : @eq (set _) _ _ |- _ ] => apply (f_equal (fun f => f x)) in H;
                                                apply eq_iff in H
               end
      end; sets0;
  try match goal with
      | [ H : @eq (set ?T) _ _, x : ?T |- _ ] =>
        repeat match goal with
               | [ H : @eq (set T) _ _ |- _ ] => apply (f_equal (fun f => f x)) in H;
                                                 apply eq_iff in H
               end;
          solve [ sets0 ]
      end.
 Ltac model_check_invert1 :=
  match goal with
  | [ H : ?P |- _ ] =>
    match type of P with
    | Prop => invert H;
              repeat match goal with
                     | [ H : existT _ ?x _ = existT _ ?x _ |- _ ] =>
                       apply inj_pair2 in H; subst
                     end; simplify
    end
  end.
 Ltac model_check_invert := simplify; subst; repeat model_check_invert1.
 Lemma oneStepClosure_solve : forall A (sys : trsys A) I I',
  oneStepClosure sys I I'
  -> I = I'
  -> oneStepClosure sys I I.
 Proof.
  equality.
 Qed.
 Ltac singletoner := try (exfalso; solve [ sets ]);
  repeat match goal with
         (* | _ => apply singleton_in *)
         | [ |- _ ?S ] => idtac S; apply singleton_in
         | [ |- (_ \cup _) _ ] => apply singleton_in_other
         end.
 Ltac closure :=
  repeat (apply oneStepClosure_empty
          || (apply oneStepClosure_split; [ model_check_invert; try equality; solve [ singletoner ] | ])).
 Ltac model_check_done :=
  apply MscDone; eapply oneStepClosure_solve; [ closure | simplify; solve [ sets ] ].
 Ltac model_check_step0 :=
  eapply MscStep; [ closure | simplify ].
 Ltac model_check_step :=
  match goal with
  | [ |- multiStepClosure _ ?inv1 _ _ ] =>
    model_check_step0;
    match goal with
    | [ |- multiStepClosure _ ?inv2 _ _ ] =>
      (assert (inv1 = inv2) by compare_sets; fail 3)
      || idtac
    end
  end.
 Ltac model_check_steps1 := model_check_step || model_check_done.
 Ltac model_check_steps := repeat model_check_steps1.
 Ltac model_check_finish := simplify; propositional; subst; simplify; try equality; try linear_arithmetic.
 Ltac model_check_infer :=
  apply multiStepClosure_ok; simplify; model_check_steps.
 Ltac model_check_find_invariant :=
  simplify; eapply invariant_weaken; [ model_check_infer | ]; cbv beta in *.
 Ltac model_check := model_check_find_invariant; model_check_finish.
 Inductive ordering (n m : nat) :=
 | Lt (_ : n < m)
 | Eq (_ : n = m)
 | Gt (_ : n > m).
 Local Hint Constructors ordering.
 Local Hint Extern 1 (_ < _) => omega.
 Local Hint Extern 1 (_ > _) => omega.
 Theorem totally_ordered : forall n m, ordering n m.
 Proof.
  induction n; destruct m; simpl; eauto.
  destruct (IHn m); eauto.
 Qed.
 Ltac total_ordering N M := destruct (totally_ordered N M).
 Ltac inList x xs :=
  match xs with
  | (x, _) => true
  | (_, ?xs') => inList x xs'
  | _ => false
  end.
 Ltac maybe_simplify_map m found kont :=
  match m with
  | @empty ?A ?B => kont (@empty A B)
  | ?m' $+ (?k, ?v) =>
    let iL := inList k found in
    match iL with
    | true => maybe_simplify_map m' found kont
    | false =>
      maybe_simplify_map m' (k, found) ltac:(fun m' => kont (m' $+ (k, v)))
    end
  end.
 Ltac simplify_map' m found kont :=
  match m with
  | ?m' $+ (?k, ?v) =>
    let iL := inList k found in
      match iL with
      | true => maybe_simplify_map m' found kont
      | false =>
        simplify_map' m' (k, found) ltac:(fun m' => kont (m' $+ (k, v)))
      end
  end.
 Ltac simplify_map :=
  match goal with
  | [ |- context[@add ?A ?B ?m ?k ?v] ] =>
    simplify_map' (m $+ (k, v)) tt ltac:(fun m' =>
                                           replace (@add A B m k v) with m' by maps_equal)
  end.
 Require Import Classical.
 Ltac excluded_middle P := destruct (classic P).
--- a/FrapWithoutSets.v
+++ b/FrapWithoutSets.v
@ -0,0 +1,373 @@
 Require Import Eqdep String Arith Omega Program Sets Relations Map Var Invariant Bool ModelCheck.
 Export String Arith Sets Relations Map Var Invariant Bool ModelCheck.
 Require Import List.
 Export List ListNotations.
 Open Scope string_scope.
 Open Scope list_scope.
 Ltac inductN n :=
  match goal with
    | [ |- forall x : ?E, _ ] =>
      match type of E with
        | Prop =>
          let H := fresh in intro H;
            match n with
              | 1 => dependent induction H
              | S ?n' => inductN n'
            end
        | _ => intro; inductN n
      end
  end.
 Ltac same_structure x y :=
  match x with
  | ?f ?a1 ?b1 ?c1 ?d1 =>
    match y with
    | f ?a2 ?b2 ?c2 ?d2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2; same_structure d1 d2
    | _ => fail 2
    end
  | ?f ?a1 ?b1 ?c1 =>
    match y with
    | f ?a2 ?b2 ?c2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2
    | _ => fail 2
    end
  | ?f ?a1 ?b1 =>
    match y with
    | f ?a2 ?b2 => same_structure a1 a2; same_structure b1 b2
    | _ => fail 2
    end
  | ?f ?a1 =>
    match y with
    | f ?a2 => same_structure a1 a2
    | _ => fail 2
    end
  | _ =>
    match y with
    | ?f ?a1 ?b1 ?c1 ?d1 =>
      match x with
      | f ?a2 ?b2 ?c2 ?d2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2; same_structure d1 d2
      | _ => fail 2
      end
    | ?f ?a1 ?b1 ?c1 =>
      match x with
      | f ?a2 ?b2 ?c2 => same_structure a1 a2; same_structure b1 b2; same_structure c1 c2
      | _ => fail 2
      end
    | ?f ?a1 ?b1 =>
      match x with
      | f ?a2 ?b2 => same_structure a1 a2; same_structure b1 b2
      | _ => fail 2
      end
    | ?f ?a1 =>
      match x with
      | f ?a2 => same_structure a1 a2
      | _ => fail 2
      end
    | _ => idtac
    end
  end.
 Ltac instantiate_obvious1 H :=
  match type of H with
  | _ ++ _ = _ ++ _ -> _ => fail 1
  | ?x = ?y -> _ =>
    (same_structure x y; specialize (H eq_refl))
    || (has_evar (x, y); fail 3)
  | JMeq.JMeq ?x ?y -> _ =>
    (same_structure x y; specialize (H JMeq.JMeq_refl))
    || (has_evar (x, y); fail 3)
  | forall x : ?T, _ =>
    match type of T with
    | Prop => fail 1
    | _ =>
      let x' := fresh x in
      evar (x' : T);
      let x'' := eval unfold x' in x' in specialize (H x''); clear x';
        instantiate_obvious1 H
    end
  end.
 Ltac instantiate_obvious H :=
  match type of H with
    | context[@eq string _  _] => idtac
    | _ => repeat instantiate_obvious1 H
  end.
 Ltac instantiate_obviouses :=
  repeat match goal with
         | [ H : _ |- _ ] => instantiate_obvious H
         end.
 Ltac induct e := (inductN e || dependent induction e); instantiate_obviouses.
 Ltac invert' H := inversion H; clear H; subst.
 Ltac invertN n :=
  match goal with
    | [ |- forall x : ?E, _ ] =>
      match type of E with
        | Prop =>
          let H := fresh in intro H;
            match n with
              | 1 => invert' H
              | S ?n' => invertN n'
            end
        | _ => intro; invertN n
      end
  end.
 Ltac invert e := invertN e || invert' e.
 Ltac invert0 e := invert e; fail.
 Ltac invert1 e := invert0 e || (invert e; []).
 Ltac invert2 e := invert1 e || (invert e; [|]).
 Ltac maps_neq :=
  match goal with
  | [ H : ?m1 = ?m2 |- _ ] =>
    let rec recur E :=
        match E with
        | ?E' $+ (?k, _) => 
          (apply (f_equal (fun m => m $? k)) in H; simpl in *; autorewrite with core in *; simpl in *; congruence)
          || recur E'
        end in
    recur m1 || recur m2
 end.
 Ltac fancy_neq :=
  repeat match goal with
         | _ => maps_neq
         | [ H : @eq (nat -> _) _ _ |- _ ] => apply (f_equal (fun f => f 0)) in H
         | [ H : @eq ?T _ _ |- _ ] =>
           match eval compute in T with
           | fmap _ _ => fail 1
           | _ => invert H
           end
         end.
 Ltac maps_equal' := progress Frap.Map.M.maps_equal; autorewrite with core; simpl.
 Ltac removeDups :=
  match goal with
  | [ |- context[constant ?ls] ] =>
    someMatch ls;
    erewrite (@removeDups_ok _ ls)
      by repeat (apply RdNil
                 || (apply RdNew; [ simpl; intuition (congruence || solve [ fancy_neq ]) | ])
                 || (apply RdDup; [ simpl; intuition (congruence || (repeat (maps_equal' || f_equal))) | ]))
  end.
 Ltac doSubtract :=
  match goal with
  | [ |- context[constant ?ls \setminus constant ?ls0] ] =>
    erewrite (@doSubtract_ok _ ls ls0)
      by repeat (apply DsNil
                 || (apply DsKeep; [ simpl; intuition (congruence || solve [ fancy_neq ]) | ])
                 || (apply DsDrop; [ simpl; intuition (congruence || (repeat (maps_equal' || f_equal))) | ]))
  end.
 Ltac simpl_maps :=
  repeat match goal with
         | [ |- context[add ?m ?k1 ?v $? ?k2] ] =>
           (rewrite (@lookup_add_ne _ _ m k1 k2 v) by (congruence || omega))
           || (rewrite (@lookup_add_eq _ _ m k1 k2 v) by (congruence || omega))
         end.
 Ltac simplify := repeat (unifyTails; pose proof I);
                repeat match goal with
                       | [ H : True |- _ ] => clear H
                       end;
                repeat progress (simpl in *; intros; try autorewrite with core in *; simpl_maps);
                                 repeat (normalize_set || doSubtract).
 Ltac propositional := intuition idtac.
 Ltac linear_arithmetic := intros;
    repeat match goal with
           | [ |- context[max ?a ?b] ] =>
             let Heq := fresh "Heq" in destruct (Max.max_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           | [ _ : context[max ?a ?b] |- _ ] =>
             let Heq := fresh "Heq" in destruct (Max.max_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           | [ |- context[min ?a ?b] ] =>
             let Heq := fresh "Heq" in destruct (Min.min_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           | [ _ : context[min ?a ?b] |- _ ] =>
             let Heq := fresh "Heq" in destruct (Min.min_spec a b) as [[? Heq] | [? Heq]];
               rewrite Heq in *; clear Heq
           end; omega.
 Ltac equality := intuition congruence.
 Ltac cases E :=
  ((is_var E; destruct E)
   || match type of E with
      | {_} + {_} => destruct E
      | _ => let Heq := fresh "Heq" in destruct E eqn:Heq
      end);
  repeat match goal with
         | [ H : _ = left _ |- _ ] => clear H
         | [ H : _ = right _ |- _ ] => clear H
         end.
 Global Opaque max min.
 Infix "==n" := eq_nat_dec (no associativity, at level 50).
 Infix "<=?" := le_lt_dec.
 Export Frap.Map.
 Ltac maps_equal := Frap.Map.M.maps_equal; simplify.
 Ltac first_order := firstorder idtac.
 (** * Model checking *)
 Lemma eq_iff : forall P Q,
    P = Q
    -> (P <-> Q).
 Proof.
  equality.
 Qed.
 Ltac sets0 := Sets.sets ltac:(simpl in *; intuition (subst; auto; try equality; try linear_arithmetic)).
 Ltac sets := propositional;
  try match goal with
      | [ |- @eq (set _) _ _ ] =>
        let x := fresh "x" in
        apply sets_equal; intro x;
        repeat match goal with
               | [ H : @eq (set _) _ _ |- _ ] => apply (f_equal (fun f => f x)) in H;
                                                apply eq_iff in H
               end
      end; sets0;
  try match goal with
      | [ H : @eq (set ?T) _ _, x : ?T |- _ ] =>
        repeat match goal with
               | [ H : @eq (set T) _ _ |- _ ] => apply (f_equal (fun f => f x)) in H;
                                                 apply eq_iff in H
               end;
          solve [ sets0 ]
      end.
 Ltac model_check_invert1 :=
  match goal with
  | [ H : ?P |- _ ] =>
    match type of P with
    | Prop => invert H;
              repeat match goal with
                     | [ H : existT _ ?x _ = existT _ ?x _ |- _ ] =>
                       apply inj_pair2 in H; subst
                     end; simplify
    end
  end.
 Ltac model_check_invert := simplify; subst; repeat model_check_invert1.
 Lemma oneStepClosure_solve : forall A (sys : trsys A) I I',
  oneStepClosure sys I I'
  -> I = I'
  -> oneStepClosure sys I I.
 Proof.
  equality.
 Qed.
 Ltac singletoner := try (exfalso; solve [ sets ]);
  repeat match goal with
         (* | _ => apply singleton_in *)
         | [ |- _ ?S ] => idtac S; apply singleton_in
         | [ |- (_ \cup _) _ ] => apply singleton_in_other
         end.
 Ltac closure :=
  repeat (apply oneStepClosure_empty
          || (apply oneStepClosure_split; [ model_check_invert; try equality; solve [ singletoner ] | ])).
 Ltac model_check_done :=
  apply MscDone; eapply oneStepClosure_solve; [ closure | simplify; solve [ sets ] ].
 Ltac model_check_step0 :=
  eapply MscStep; [ closure | simplify ].
 Ltac model_check_step :=
  match goal with
  | [ |- multiStepClosure _ ?inv1 _ _ ] =>
    model_check_step0;
    match goal with
    | [ |- multiStepClosure _ ?inv2 _ _ ] =>
      (assert (inv1 = inv2) by compare_sets; fail 3)
      || idtac
    end
  end.
 Ltac model_check_steps1 := model_check_step || model_check_done.
 Ltac model_check_steps := repeat model_check_steps1.
 Ltac model_check_finish := simplify; propositional; subst; simplify; try equality; try linear_arithmetic.
 Ltac model_check_infer :=
  apply multiStepClosure_ok; simplify; model_check_steps.
 Ltac model_check_find_invariant :=
  simplify; eapply invariant_weaken; [ model_check_infer | ]; cbv beta in *.
 Ltac model_check := model_check_find_invariant; model_check_finish.
 Inductive ordering (n m : nat) :=
 | Lt (_ : n < m)
 | Eq (_ : n = m)
 | Gt (_ : n > m).
 Local Hint Constructors ordering.
 Local Hint Extern 1 (_ < _) => omega.
 Local Hint Extern 1 (_ > _) => omega.
 Theorem totally_ordered : forall n m, ordering n m.
 Proof.
  induction n; destruct m; simpl; eauto.
  destruct (IHn m); eauto.
 Qed.
 Ltac total_ordering N M := destruct (totally_ordered N M).
 Ltac inList x xs :=
  match xs with
  | (x, _) => true
  | (_, ?xs') => inList x xs'
  | _ => false
  end.
 Ltac maybe_simplify_map m found kont :=
  match m with
  | @empty ?A ?B => kont (@empty A B)
  | ?m' $+ (?k, ?v) =>
    let iL := inList k found in
    match iL with
    | true => maybe_simplify_map m' found kont
    | false =>
      maybe_simplify_map m' (k, found) ltac:(fun m' => kont (m' $+ (k, v)))
    end
  end.
 Ltac simplify_map' m found kont :=
  match m with
  | ?m' $+ (?k, ?v) =>
    let iL := inList k found in
      match iL with
      | true => maybe_simplify_map m' found kont
      | false =>
        simplify_map' m' (k, found) ltac:(fun m' => kont (m' $+ (k, v)))
      end
  end.
 Ltac simplify_map :=
  match goal with
  | [ |- context[@add ?A ?B ?m ?k ?v] ] =>
    simplify_map' (m $+ (k, v)) tt ltac:(fun m' =>
                                           replace (@add A B m k v) with m' by maps_equal)
  end.
 Require Import Classical.
 Ltac excluded_middle P := destruct (classic P).
--- a/Map.v
+++ b/Map.v
@ -64,7 +64,7 @@ Module Type S.
    -> (m1 $++ m2) $? k = m2 $? k.
  Axiom join_comm : forall A B (m1 m2 : fmap A B),
-    dom m1 \cap dom m2 = {}
+    dom m1 \cap dom m2 = constant nil
    -> m1 $++ m2 = m2 $++ m1.
  Axiom join_assoc : forall A B (m1 m2 m3 : fmap A B),
@ -116,10 +116,10 @@ Module Type S.
  Axiom empty_includes : forall A B (m : fmap A B), empty A B $<= m.
-  Axiom dom_empty : forall A B, dom (empty A B) = {}.
+  Axiom dom_empty : forall A B, dom (empty A B) = constant nil.
  Axiom dom_add : forall A B (m : fmap A B) (k : A) (v : B),
-    dom (add m k v) = {k} \cup dom m.
+    dom (add m k v) = constant (k :: nil) \cup dom m.
  Axiom lookup_restrict_true : forall A B (P : A -> Prop) (m : fmap A B) k,
    P k
@ -390,7 +390,7 @@ Module M : S.
  Qed.
  Theorem join_comm : forall A B (m1 m2 : fmap A B),
-    dom m1 \cap dom m2 = {}
+    dom m1 \cap dom m2 = constant nil
    -> join m1 m2 = join m2 m1.
  Proof.
    intros; apply fmap_ext; unfold join, lookup; intros.
@ -508,13 +508,13 @@ Module M : S.
    unfold includes, empty; intuition congruence.
  Qed.
-  Theorem dom_empty : forall A B, dom (empty (A := A) B) = {}.
+  Theorem dom_empty : forall A B, dom (empty (A := A) B) = constant nil.
  Proof.
    unfold dom, empty; intros; sets idtac.
  Qed.
  Theorem dom_add : forall A B (m : fmap A B) (k : A) (v : B),
-    dom (add m k v) = {k} \cup dom m.
+    dom (add m k v) = constant (k :: nil) \cup dom m.
  Proof.
    unfold dom, add; simpl; intros.
    sets ltac:(simpl in *; try match goal with
--- a/MessagesAndRefinement.v
+++ b/MessagesAndRefinement.v
@ -10,7 +10,7 @@ Set Asymmetric Patterns.
 (** * First, an unexplained tactic that will come in handy.... *)
-Ltac invert H := (Frap.invert H || (inversion H; clear H));
+Ltac invert H := (FrapWithoutSets.invert H || (inversion H; clear H));
                 repeat match goal with
                        | [ x : _ |- _ ] => subst x
                        | [ H : existT _ _ _ = existT _ _ _ |- _ ] => apply inj_pair2 in H; try subst
--- a/ModelCheck.v
+++ b/ModelCheck.v
@ -75,7 +75,7 @@ Qed.
 Theorem oneStepClosure_split : forall state (sys : trsys state) st sts (inv1 inv2 : state -> Prop),
  (forall st', sys.(Step) st st' -> inv1 st')
  -> oneStepClosure sys (constant sts) inv2
-  -> oneStepClosure sys (constant (st :: sts)) ({st} \cup inv1 \cup inv2).
+  -> oneStepClosure sys (constant (st :: sts)) (constant (st :: nil) \cup inv1 \cup inv2).
 Proof.
  unfold oneStepClosure, oneStepClosure_current, oneStepClosure_new; intuition.
@ -89,7 +89,7 @@ Proof.
 Qed.
 Theorem singleton_in : forall {A} (x : A) rest,
-  ({x} \cup rest) x.
+  (constant (x :: nil) \cup rest) x.
 Proof.
  unfold union; simpl; auto.
 Qed.
--- a/README.md
+++ b/README.md
@ -28,3 +28,7 @@ The main narrative, also present in the book PDF, presents standard program-proo
 * Chapter 15: `SharedMemory.v`
 * Chapter 16: `ConcurrentSeparationLogic.v`
 * Chapter 17: `MessagesAndRefinement.v`
 There are also two supplementary files that are independent of the main narrative, for introducing programming with dependent types, a distinctive Coq feature that we neither use nor recommend for the problem sets, but which many students find interesting (and useful in other contexts).
 * `SubsetTypes.v`: a first introduction to dependent types by attaching predicates to normal types (used after `CompilerCorrectness.v` in the last course offering)
 * One more coming soon
--- a/Sets.v
+++ b/Sets.v
@ -35,8 +35,6 @@ Section set.
 End set.
 Infix "\in" := In (at level 70).
 Notation "{ }" := (constant nil).
 Notation "{ x1 , .. , xN }" := (constant (cons x1 (.. (cons xN nil) ..))).
 Notation "[ P ]" := (check P).
 Infix "\cup" := union (at level 40).
 Infix "\cap" := intersection (at level 40).
@ -45,6 +43,14 @@ Infix "\subseteq" := subseteq (at level 70).
 Infix "\subset" := subset (at level 70).
 Notation "[ x | P ]" := (scomp (fun x => P)).
 Module Type EMPTY.
 End EMPTY.
 Module SetNotations(M : EMPTY).
  Notation "{ }" := (constant nil).
  Notation "{ x1 , .. , xN }" := (constant (cons x1 (.. (cons xN nil) ..))).
 End SetNotations.
 Ltac sets' tac :=
  unfold In, constant, universe, check, union, intersection, minus, complement, subseteq, subset, scomp in *;
    tauto || intuition tac.
@ -288,7 +294,7 @@ Section setexpr.
    match e with
    | Literal vs =>
      match env with
-      | [] => {}
+      | [] => constant []
      | x :: _ => constant (map (nth_default x env) vs)
      end
    | Constant s => s
@ -339,7 +345,7 @@ Section setexpr.
  Definition interp_normal_form (env : list A) (nf : normal_form) : set A :=
    let cs := match env with
-              | [] => {}
+              | [] => constant []
              | x :: _ => constant (map (nth_default x env) nf.(Elements))
              end in
    match nf.(Other) with
@ -557,7 +563,7 @@ Ltac quote E env k :=
            quote' E2 env' ltac:(fun e2 env'' =>
              k (Union e1 e2) env''))
        | _ =>
-          (let pf := constr:(eq_refl : E = {}) in
+          (let pf := constr:(eq_refl : E = constant []) in
           k (Literal A []) env)
          || k (Constant E) env
        end in
--- a/SubsetTypes.v
+++ b/SubsetTypes.v
@ -0,0 +1,633 @@
 (** Formal Reasoning About Programs <http://adam.chlipala.net/frap/>
  * Supplementary Coq material: subset types
  * Author: Adam Chlipala
  * License: https://creativecommons.org/licenses/by-nc-nd/4.0/
  * Much of the material comes from CPDT <http://adam.chlipala.net/cpdt/> by the same author. *)
 Require Import FrapWithoutSets.
 (* We import a pared-down version of the book library, to avoid notations that
 * clash with some we want to use here. *)
 Set Implicit Arguments.
 Set Asymmetric Patterns.
 (* Compatibility flag that affects pattern matching for fancy types *)
 (* So far, we have seen many examples of what we might call "classical program
 * verification."  We write programs, write their specifications, and then prove
 * that the programs satisfy their specifications.  The programs that we have
 * written in Coq have been normal functional programs that we could just as
 * well have written in Haskell or ML.  In this lecture, we start investigating
 * uses of _dependent types_ to integrate programming, specification, and
 * proving into a single phase.  The techniques we will learn make it possible
 * to reduce the cost of program verification dramatically. *)
 (** * Introducing Subset Types *)
 (** Let us consider several ways of implementing the natural-number-predecessor
 * function.  We start by displaying the definition from the standard library: *)
 Compute pred.
 (* We can use a new command, [Extraction], to produce an OCaml version of this
 * function. *)
 Extraction pred.
 (* Returning 0 as the predecessor of 0 can come across as somewhat of a hack.
 * In some situations, we might like to be sure that we never try to take the
 * predecessor of 0.  We can enforce this by giving [pred] a stronger, dependent
 * type. *)
 Lemma zgtz : 0 > 0 -> False.
 Proof.
  linear_arithmetic.
 Qed.
 Definition pred_strong1 (n : nat) : n > 0 -> nat :=
  match n with
    | O => fun pf : 0 > 0 => match zgtz pf with end
    | S n' => fun _ => n'
  end.
 (* We expand the type of [pred] to include a _proof_ that its argument [n] is
 * greater than 0.  When [n] is 0, we use the proof to derive a contradiction,
 * which we can use to build a value of any type via a vacuous pattern match.
 * When [n] is a successor, we have no need for the proof and just return the
 * answer.  The proof argument can be said to have a _dependent_ type, because
 * its type depends on the _value_ of the argument [n].
 *
 * Coq's [Compute] command can execute particular invocations of [pred_strong1]
 * just as easily as it can execute more traditional functional programs. *)
 Theorem two_gt0 : 2 > 0.
 Proof.
  linear_arithmetic.
 Qed.
 Compute pred_strong1 two_gt0.
 (* One aspect in particular of the definition of [pred_strong1] may be
 * surprising.  We took advantage of [Definition]'s syntactic sugar for defining
 * function arguments in the case of [n], but we bound the proofs later with
 * explicit [fun] expressions.  Let us see what happens if we write this
 * function in the way that at first seems most natural. *)
 Fail Definition pred_strong1' (n : nat) (pf : n > 0) : nat :=
  match n with
    | O => match zgtz pf with end
    | S n' => n'
  end.
 (* The term [zgtz pf] fails to type-check.  Somehow the type checker has failed
 * to take into account information that follows from which [match] branch that
 * term appears in.  The problem is that, by default, [match] does not let us
 * use such implied information.  To get refined typing, we must always rely on
 * [match] annotations, either written explicitly or inferred.
 *
 * In this case, we must use a [return] annotation to declare the relationship
 * between the _value_ of the [match] discriminee and the _type_ of the result.
 * There is no annotation that lets us declare a relationship between the
 * discriminee and the type of a variable that is already in scope; hence, we
 * delay the binding of [pf], so that we can use the [return] annotation to
 * express the needed relationship.
 *
 * We are lucky that Coq's heuristics infer the [return] clause (specifically,
 * [return n > 0 -> nat]) for us in the definition of [pred_strong1], leading to
 * the following elaborated code: *)
 Definition pred_strong1' (n : nat) : n > 0 -> nat :=
  match n return n > 0 -> nat with
    | O => fun pf : 0 > 0 => match zgtz pf with end
    | S n' => fun _ => n'
  end.
 (* By making explicit the functional relationship between value [n] and the
 * result type of the [match], we guide Coq toward proper type checking.  The
 * clause for this example follows by simple copying of the original annotation
 * on the definition.  In general, however, the [match] annotation inference
 * problem is undecidable.  The known undecidable problem of
 * _higher-order unification_ reduces to the [match] type inference problem.
 * Over time, Coq is enhanced with more and more heuristics to get around this
 * problem, but there must always exist [match]es whose types Coq cannot infer
 * without annotations.
 *
 * Let us now take a look at the OCaml code Coq generates for [pred_strong1]. *)
 Extraction pred_strong1.
 (* The proof argument has disappeared!  We get exactly the OCaml code we would
 * have written manually.  This is our first demonstration of the main
 * technically interesting feature of Coq program extraction: proofs are erased
 * systematically.
 *
 * We can reimplement our dependently typed [pred] based on _subset types_,
 * defined in the standard library with the type family %[sig]. *)
 Print sig.
 (* We rewrite [pred_strong1], using some syntactic sugar for subset types, after
 * we deactivate some clashing notations for set literals. *)
 Locate "{ _ : _ | _ }".
 Definition pred_strong2 (s : {n : nat | n > 0} ) : nat :=
  match s with
    | exist O pf => match zgtz pf with end
    | exist (S n') _ => n'
  end.
 (* To build a value of a subset type, we use the [exist] constructor, and the
 * details of how to do that follow from the output of our earlier [Print sig]
 * command, where we elided the extra information that parameter [A] is
 * implicit.  We need an extra [_] here and not in the definition of
 * [pred_strong2] because _parameters_ of inductive types (like the predicate
 * [P] for [sig]) are not mentioned in pattern matching, but _are_ mentioned in
 * construction of terms (if they are not marked as implicit arguments).
 * (Actually, this behavior changed between Coq versions 8.4 and 8.5, hence the
 * near at the top of the file to revert to the old behavior.) *)
 Compute pred_strong2 (exist _ 2 two_gt0).
 Extraction pred_strong2.
 (* We arrive at the same OCaml code as was extracted from [pred_strong1], which
 * may seem surprising at first.  The reason is that a value of [sig] is a pair
 * of two pieces, a value and a proof about it.  Extraction erases the proof,
 * which reduces the constructor [exist] of [sig] to taking just a single
 * argument.  An optimization eliminates uses of datatypes with single
 * constructors taking single arguments, and we arrive back where we started.
 *
 * We can continue on in the process of refining [pred]'s type.  Let us change
 * its result type to capture that the output is really the predecessor of the
 * input. *)
 Definition pred_strong3 (s : {n : nat | n > 0}) : {m : nat | proj1_sig s = S m} :=
  match s return {m : nat | proj1_sig s = S m} with
    | exist 0 pf => match zgtz pf with end
    | exist (S n') pf => exist _ n' (eq_refl _)
  end.
 Compute pred_strong3 (exist _ 2 two_gt0).
 (* A value in a subset type can be thought of as a _dependent pair_ (or
 * _sigma type_ of a base value and a proof about it.  The function [proj1_sig]
 * extracts the first component of the pair.  It turns out that we need to
 * include an explicit [return] clause here, since Coq's heuristics are not
 * smart enough to propagate the result type that we wrote earlier.
 *
 * By now, the reader is probably ready to believe that the new [pred_strong]
 * leads to the same OCaml code as we have seen several times so far, and Coq
 * does not disappoint. *)
 Extraction pred_strong3.
 (* We have managed to reach a type that is, in a formal sense, the most
 * expressive possible for [pred].  Any other implementation of the same type
 * must have the same input-output behavior.  However, there is still room for
 * improvement in making this kind of code easier to write.  Here is a version
 * that takes advantage of tactic-based theorem proving.  We switch back to
 * passing a separate proof argument instead of using a subset type for the
 * function's input, because this leads to cleaner code.  ([False_rec] is a
 * library function that can be used to produce a value in any type given a
 * proof of [False].  It's defined in terms of the vacuous pattern match we saw
 * earlier.) *)
 Definition pred_strong4 : forall (n : nat), n > 0 -> {m : nat | n = S m}.
  refine (fun n =>
    match n with
      | O => fun _ => False_rec _ _
      | S n' => fun _ => exist _ n' _
    end).
  (* We build [pred_strong4] using tactic-based proving, beginning with a
   * [Definition] command that ends in a period before a definition is given.
   * Such a command enters the interactive proving mode, with the type given for
   * the new identifier as our proof goal.
   *
   * We do most of the work with the [refine] tactic, to which we pass a partial
   * "proof" of the type we are trying to prove.  There may be some pieces left
   * to fill in, indicated by underscores.  Any underscore that Coq cannot
   * reconstruct with type inference is added as a proof subgoal.  In this case,
   * we have two subgoals.
   *
   * We can see that the first subgoal comes from the second underscore passed
   * to [False_rec], and the second subgoal comes from the second underscore
   * passed to [exist].  In the first case, we see that, though we bound the
   * proof variable with an underscore, it is still available in our proof
   * context.  It is hard to refer to underscore-named variables in manual
   * proofs, but automation makes short work of them.  Both subgoals are easy to
   * discharge that way, so let us back up and ask to prove all subgoals
   * automatically. *)
  Undo.
  refine (fun n =>
    match n with
      | O => fun _ => False_rec _ _
      | S n' => fun _ => exist _ n' _
    end); equality || linear_arithmetic.
 Defined.
 (* We end the "proof" with [Defined] instead of [Qed], so that the definition we
 * constructed remains visible.  This contrasts to the case of ending a proof
 * with [Qed], where the details of the proof are hidden afterward.  (More
 * formally, [Defined] marks an identifier as _transparent_, allowing it to be
 * unfolded; while [Qed] marks an identifier as _opaque_, preventing unfolding.)
 * Let us see what our proof script constructed. *)
 Print pred_strong4.
 (* We see the code we entered, with some (pretty long!) proofs filled in. *)
 Compute pred_strong4 two_gt0.
 (* We are almost done with the ideal implementation of dependent predecessor.
 * We can use Coq's syntax extension facility to arrive at code with almost no
 * complexity beyond a Haskell or ML program with a complete specification in a
 * comment.  In this book, we will not dwell on the details of syntax
 * extensions; the Coq manual gives a straightforward introduction to them. *)
 Notation "!" := (False_rec _ _).
 Notation "[ e ]" := (exist _ e _).
 Definition pred_strong5 : forall (n : nat), n > 0 -> {m : nat | n = S m}.
  refine (fun n =>
    match n with
      | O => fun _ => !
      | S n' => fun _ => [n']
    end); equality || linear_arithmetic.
 Defined.
 (* By default, notations are also used in pretty-printing terms, including
 * results of evaluation. *)
 Compute pred_strong5 two_gt0.
 (** * Decidable Proposition Types *)
 (* There is another type in the standard library that captures the idea of
 * program values that indicate which of two propositions is true. *)
 Print sumbool.
 (* Here, the constructors of [sumbool] have types written in terms of a
 * registered notation for [sumbool], such that the result type of each
 * constructor desugars to [sumbool A B].  We can define some notations of our
 * own to make working with [sumbool] more convenient. *)
 Notation "'Yes'" := (left _ _).
 Notation "'No'" := (right _ _).
 Notation "'Reduce' x" := (if x then Yes else No) (at level 50).
 (* The [Reduce] notation is notable because it demonstrates how [if] is
 * overloaded in Coq.  The [if] form actually works when the test expression has
 * any two-constructor inductive type.  Moreover, in the [then] and [else]
 * branches, the appropriate constructor arguments are bound.  This is important
 * when working with [sumbool]s, when we want to have the proof stored in the
 * test expression available when proving the proof obligations generated in the
 * appropriate branch.
 *
 * Now we can write [eq_nat_dec], which compares two natural numbers, returning
 * either a proof of their equality or a proof of their inequality. *)
 Definition eq_nat_dec : forall n m : nat, {n = m} + {n <> m}.
  refine (fix f (n m : nat) : {n = m} + {n <> m} :=
    match n, m with
      | O, O => Yes
      | S n', S m' => Reduce (f n' m')
      | _, _ => No
    end); equality.
 Defined.
 Compute eq_nat_dec 2 2.
 Compute eq_nat_dec 2 3.
 (* Note that the [Yes] and [No] notations are hiding proofs establishing the
 * correctness of the outputs.
 *
 * Our definition extracts to reasonable OCaml code. *)
 Extraction eq_nat_dec.
 (* Proving this kind of decidable equality result is so common that Coq comes
 * with a tactic for automating it. *)
 Definition eq_nat_dec' (n m : nat) : {n = m} + {n <> m}.
  decide equality.
 Defined.
 (* Curious readers can verify that the [decide equality] version extracts to the
 * same OCaml code as our more manual version does.  That OCaml code had one
 * undesirable property, which is that it uses [Left] and [Right] constructors
 * instead of the Boolean values built into OCaml.  We can fix this, by using
 * Coq's facility for mapping Coq inductive types to OCaml variant types. *)
 Extract Inductive sumbool => "bool" ["true" "false"].
 Extraction eq_nat_dec'.
 (* We can build "smart" versions of the usual Boolean operators and put them to
 * good use in certified programming.  For instance, here is a [sumbool] version
 * of Boolean "or." *)
 Notation "x || y" := (if x then Yes else Reduce y).
 (* Let us use it for building a function that decides list membership.  We need
 * to assume the existence of an equality decision procedure for the type of
 * list elements. *)
 Section In_dec.
  Variable A : Set.
  Variable A_eq_dec : forall x y : A, {x = y} + {x <> y}.
  (* The final function is easy to write using the techniques we have developed
   * so far. *)
  Definition In_dec : forall (x : A) (ls : list A), {In x ls} + {~ In x ls}.
    refine (fix f (x : A) (ls : list A) : {In x ls} + {~ In x ls} :=
      match ls with
 	| nil => No
 	| x' :: ls' => A_eq_dec x x' || f x ls'
      end); simplify; equality.
  Defined.
 End In_dec.
 Compute In_dec eq_nat_dec 2 (1 :: 2 :: nil).
 Compute In_dec eq_nat_dec 3 (1 :: 2 :: nil).
 (* The [In_dec] function has a reasonable extraction to OCaml. *)
 Extraction In_dec.
 (* This is more or the less code for the corresponding function from the OCaml
 * standard library. *)
 (** * Partial Subset Types *)
 (* Our final implementation of dependent predecessor used a very specific
 * argument type to ensure that execution could always complete normally.
 * Sometimes we want to allow execution to fail, and we want a more principled
 * way of signaling failure than returning a default value, as [pred] does for
 * [0].  One approach is to define this type family [maybe], which is a version
 * of [sig] that allows obligation-free failure. *)
 Inductive maybe (A : Set) (P : A -> Prop) : Set :=
 | Unknown : maybe P
 | Found : forall x : A, P x -> maybe P.
 (* We can define some new notations, analogous to those we defined for subset
 * types. *)
 Notation "{{ x | P }}" := (maybe (fun x => P)).
 Notation "??" := (Unknown _).
 Notation "[| x |]" := (Found _ x _).
 (* Now our next version of [pred] is trivial to write. *)
 Definition pred_strong7 : forall n : nat, {{m | n = S m}}.
  refine (fun n =>
    match n return {{m | n = S m}} with
      | O => ??
      | S n' => [|n'|]
    end); trivial.
 Defined.
 Compute pred_strong7 2.
 Compute pred_strong7 0.
 (* Because we used [maybe], one valid implementation of the type we gave
 * [pred_strong7] would return [??] in every case.  We can strengthen the type
 * to rule out such vacuous implementations, and the type family [sumor] from
 * the standard library provides the easiest starting point.  For type [A] and
 * proposition [B], [A + {B}] desugars to [sumor A B], whose values are either
 * values of [A] or proofs of [B]. *)
 Print sumor.
 (* We add notations for easy use of the [sumor] constructors.  The second
 * notation is specialized to [sumor]s whose [A] parameters are instantiated
 * with regular subset types, since this is how we will use [sumor] below. *)
 Notation "!!" := (inright _ _).
 Notation "[|| x ||]" := (inleft _ [x]).
 (* Now we are ready to give the final version of possibly failing predecessor.
 * The [sumor]-based type that we use is maximally expressive; any
 * implementation of the type has the same input-output behavior. *)
 Definition pred_strong8 : forall n : nat, {m : nat | n = S m} + {n = 0}.
  refine (fun n =>
    match n with
      | O => !!
      | S n' => [||n'||]
    end); trivial.
 Defined.
 Compute pred_strong8 2.
 Compute pred_strong8 0.
 (* As with our other maximally expressive [pred] function, we arrive at quite
 * simple output values, thanks to notations. *)
 (** * Monadic Notations *)
 (* We can treat [maybe] like a monad, in the same way that the Haskell [Maybe]
 * type is interpreted as a failure monad.  Our [maybe] has the wrong type to be
 * a literal monad, but a "bind"-like notation will still be helpful. *)
 Notation "x <- e1 ; e2" := (match e1 with
                             | Unknown => ??
                             | Found x _ => e2
                           end)
 (right associativity, at level 60).
 (* The meaning of [x <- e1; e2] is: First run [e1].  If it fails to find an
 * answer, then announce failure for our derived computation, too.  If [e1]
 * _does_ find an answer, pass that answer on to [e2] to find the final result.
 * The variable [x] can be considered bound in [e2].
 *
 * This notation is very helpful for composing richly typed procedures.  For
 * instance, here is a very simple implementation of a function to take the
 * predecessors of two naturals at once. *)
 Definition doublePred : forall n1 n2 : nat, {{p | n1 = S (fst p) /\ n2 = S (snd p)}}.
  refine (fun n1 n2 =>
    m1 <- pred_strong7 n1;
    m2 <- pred_strong7 n2;
    [|(m1, m2)|]); propositional.
 Defined.
 (* We can build a [sumor] version of the "bind" notation and use it to write a
 * similarly straightforward version of this function. *)
 Notation "x <-- e1 ; e2" := (match e1 with
                               | inright _ => !!
                               | inleft (exist x _) => e2
                             end)
 (right associativity, at level 60).
 Definition doublePred' : forall n1 n2 : nat,
  {p : nat * nat | n1 = S (fst p) /\ n2 = S (snd p)}
  + {n1 = 0 \/ n2 = 0}.
  refine (fun n1 n2 =>
    m1 <-- pred_strong8 n1;
    m2 <-- pred_strong8 n2;
    [||(m1, m2)||]); propositional.
 Defined.
 (* This example demonstrates how judicious selection of notations can hide
 * complexities in the rich types of programs. *)
 (** * A Type-Checking Example *)
 (* We can apply these specification types to build a certified type checker for
 * a simple expression language. *)
 Inductive exp :=
 | Nat (n : nat)
 | Plus (e1 e2 : exp)
 | Bool (b : bool)
 | And (e1 e2 : exp).
 (* We define a simple language of types and its typing rules. *)
 Inductive type := TNat | TBool.
 Inductive hasType : exp -> type -> Prop :=
 | HtNat : forall n,
  hasType (Nat n) TNat
 | HtPlus : forall e1 e2,
  hasType e1 TNat
  -> hasType e2 TNat
  -> hasType (Plus e1 e2) TNat
 | HtBool : forall b,
  hasType (Bool b) TBool
 | HtAnd : forall e1 e2,
  hasType e1 TBool
  -> hasType e2 TBool
  -> hasType (And e1 e2) TBool.
 (* It will be helpful to have a function for comparing two types.  We build one
 * using [decide equality]. *)
 Definition eq_type_dec : forall t1 t2 : type, {t1 = t2} + {t1 <> t2}.
  decide equality.
 Defined.
 (* Another notation complements the monadic notation for [maybe] that we defined
 * earlier.  Sometimes we want to include "assertions" in our procedures.  That
 * is, we want to run a decision procedure and fail if it fails; otherwise, we
 * want to continue, with the proof that it produced made available to us.  This
 * infix notation captures that idea, for a procedure that returns an arbitrary
 * two-constructor type. *)
 Notation "e1 ;; e2" := (if e1 then e2 else ??)
  (right associativity, at level 60).
 (* With that notation defined, we can implement a [typeCheck] function, whose
 * code is only more complex than what we would write in ML because it needs to
 * include some extra type annotations.  Every [[|e|]] expression adds a
 * [hasType] proof obligation, and [eauto] makes short work of them when we add
 * [hasType]'s constructors as hints. *)
 Hint Constructors hasType.
 Definition typeCheck : forall e : exp, {{t | hasType e t}}.
  refine (fix F (e : exp) : {{t | hasType e t}} :=
    match e return {{t | hasType e t}} with
      | Nat _ => [|TNat|]
      | Plus e1 e2 =>
        t1 <- F e1;
        t2 <- F e2;
        eq_type_dec t1 TNat;;
        eq_type_dec t2 TNat;;
        [|TNat|]
      | Bool _ => [|TBool|]
      | And e1 e2 =>
        t1 <- F e1;
        t2 <- F e2;
        eq_type_dec t1 TBool;;
        eq_type_dec t2 TBool;;
        [|TBool|]
    end); subst; eauto.
 Defined.
 (* Despite manipulating proofs, our type checker is easy to run. *)
 Compute typeCheck (Nat 0).
 Compute typeCheck (Plus (Nat 1) (Nat 2)).
 Compute typeCheck (Plus (Nat 1) (Bool false)).
 (* The type checker also extracts to some reasonable OCaml code. *)
 Extraction typeCheck.
 (* We can adapt this implementation to use [sumor], so that we know our type-checker
 * only fails on ill-typed inputs.  First, we define an analogue to the
 * "assertion" notation. *)
 Notation "e1 ;;; e2" := (if e1 then e2 else !!)
  (right associativity, at level 60).
 (* Next, we prove a helpful lemma, which states that a given expression can have
 * at most one type. *)
 Lemma hasType_det : forall e t1,
  hasType e t1
  -> forall t2, hasType e t2
    -> t1 = t2.
 Proof.
  induct 1; invert 1; equality.
 Qed.
 (* Now we can define the type-checker.  Its type expresses that it only fails on
 * untypable expressions. *)
 Hint Resolve hasType_det.
 (* The lemma [hasType_det] will also be useful for proving proof obligations
 * with contradictory contexts. *)
 Definition typeCheck' : forall e : exp, {t : type | hasType e t} + {forall t, ~ hasType e t}.
  (* Finally, the implementation of [typeCheck] can be transcribed literally,
   * simply switching notations as needed. *)
  refine (fix F (e : exp) : {t : type | hasType e t} + {forall t, ~ hasType e t} :=
    match e return {t : type | hasType e t} + {forall t, ~ hasType e t} with
      | Nat _ => [||TNat||]
      | Plus e1 e2 =>
        t1 <-- F e1;
        t2 <-- F e2;
        eq_type_dec t1 TNat;;;
        eq_type_dec t2 TNat;;;
        [||TNat||]
      | Bool _ => [||TBool||]
      | And e1 e2 =>
        t1 <-- F e1;
        t2 <-- F e2;
        eq_type_dec t1 TBool;;;
        eq_type_dec t2 TBool;;;
        [||TBool||]
    end); simplify; propositional; subst; eauto;
    match goal with
    | [ H : hasType _ _ |- _ ] => invert2 H
    end; eauto.
 Defined.
 (* The short implementation here hides just how time-saving automation is.
 * Every use of one of the notations adds a proof obligation, giving us 12 in
 * total.  Most of these obligations require inversions and either uses of
 * [hasType_det] or applications of [hasType] rules.
 *
 * Our new function remains easy to test: *)
 Compute typeCheck' (Nat 0).
 Compute typeCheck' (Plus (Nat 1) (Nat 2)).
 Compute typeCheck' (Plus (Nat 1) (Bool false)).
 (* The results of simplifying calls to [typeCheck'] look deceptively similar to
 * the results for [typeCheck], but now the types of the results provide more
 * information. *)
--- a/2
+++ b/2
@ -7,6 +7,7 @@ Invariant.v
 ModelCheck.v
 Imp.v
 AbstractInterpret.v
 FrapWithoutSets.v
 Frap.v
 BasicSyntax_template.v
 BasicSyntax.v
@ -31,6 +32,7 @@ LogicProgramming_template.v
 AbstractInterpretation.v
 CompilerCorrectness.v
 CompilerCorrectness_template.v
 SubsetTypes.v
 LambdaCalculusAndTypeSoundness_template.v
 LambdaCalculusAndTypeSoundness.v
 TypesAndMutation.v