This file collects a number of basic lemmas and tactics for better proof automation, structuring large proofs, or rewriting. Most of the rewriting support is ported from ss-reflect.
Symbols starting with vlib__ are internal.

Require Import Logic.Eqdep.
Require Import Bool.
Require Import Arith.
Require Import ZArith.
Require Import String.

Open Scope bool_scope.
Open Scope list_scope.

Set Implicit Arguments.
Unset Strict Implicit.

Axioms


Require ClassicalFacts.
Require Export FunctionalExtensionality.
Require Export ProofIrrelevance.

Ltac exten := apply functional_extensionality.

Coersion of bool into Prop


Coersion of bools into Prop
Coercion is_true (b : bool) : Prop := b = true.

Hints for auto
Lemma vlib__true_is_true : true.
Proof. reflexivity. Qed.

Lemma vlib__not_false_is_true : ¬ false.
Proof. discriminate. Qed.

Hint Resolve vlib__true_is_true vlib__not_false_is_true.

Very basic automation


Set up for basic simplification

Create HintDb vlib discriminated.

Adaptation of the ss-reflect "done" tactic.

Ltac vlib__basic_done :=
  solve [trivial with vlib | apply sym_equal; trivial | discriminate | contradiction].

Ltac done := trivial with vlib; hnf; intros;
  solve [try vlib__basic_done; split;
         try vlib__basic_done; split;
         try vlib__basic_done; split;
         try vlib__basic_done; split;
         try vlib__basic_done; split; vlib__basic_done
    | match goal with H : ¬ _ |- _solve [case H; trivial] end].

A variant of the ssr "done" tactic that performs "eassumption".

Ltac edone := try eassumption; trivial; hnf; intros;
  solve [try eassumption; try vlib__basic_done; split;
         try eassumption; try vlib__basic_done; split;
         try eassumption; try vlib__basic_done; split;
         try eassumption; try vlib__basic_done; split;
         try eassumption; try vlib__basic_done; split;
         try eassumption; vlib__basic_done
    | match goal with H : ¬ _ |- _solve [case H; trivial] end].

Tactic Notation "by" tactic(tac) := (tac; done).
Tactic Notation "eby" tactic(tac) := (tac; edone).

Boolean reflection


These definitions are ported from ssr-bool.
Negation lemmas
Section NegationLemmas.

  Variables (b c : bool).

  Lemma negbT : b = false negb b.
  Proof. by case b. Qed.
  Lemma negbTE: negb b b = false.
  Proof. by case b. Qed.
  Lemma negbF : b negb b = false.
  Proof. by case b. Qed.
  Lemma negbFE: negb b = false b.
  Proof. by case b. Qed.
  Lemma negbNE: negb (negb b) b.
  Proof. by case b. Qed.

  Lemma negbLR : b = negb c negb b = c.
  Proof. by case c; intro X; rewrite X. Qed.

  Lemma negbRL : negb b = c b = negb c.
  Proof. by case b; intro X; rewrite <- X. Qed.

  Lemma contra : (c b) negb b negb c.
  Proof. by case b; case c. Qed.

End NegationLemmas.

Lemmas for ifs, which allow reasoning about the condition without repeating it inside the proof.
Section BoolIf.

Variables (A B : Type) (x : A) (f : A B) (b : bool) (vT vF : A).

Inductive if_spec : A bool Set :=
  | IfSpecTrue : b if_spec vT true
  | IfSpecFalse : b = false if_spec vF false.

Lemma ifP : if_spec (if b then vT else vF) b.
Proof. by case_eq b; constructor. Qed.

Lemma if_same : (if b then vT else vT) = vT.
Proof. by case b. Qed.

Lemma if_neg : (if negb b then vT else vF) = if b then vF else vT.
Proof. by case b. Qed.

Lemma fun_if : f (if b then vT else vF) = if b then f vT else f vF.
Proof. by case b. Qed.

Lemma if_arg : fT fF : A B,
  (if b then fT else fF) x = if b then fT x else fF x.
Proof. by case b. Qed.

End BoolIf.

The reflection predicate
Inductive reflect (P : Prop) : bool Set :=
  | ReflectT : P reflect P true
  | ReflectF : ¬ P reflect P false.

Internal reflection lemmas
Section ReflectCore.

Variables (P : Prop) (b : bool) (Hb : reflect P b) (Q : Prop) (c : bool).

Lemma introNTF : (if c then ¬ P else P) negb b = c.
Proof. by case c; case Hb. Qed.

Lemma introTF : (if c then P else ¬ P) b = c.
Proof. by case c; case Hb. Qed.

Lemma elimNTF : negb b = c if c then ¬ P else P.
Proof. by intro X; rewrite <- X; case Hb. Qed.

Lemma elimTF : b = c if c then P else ¬ P.
Proof. by intro X; rewrite <- X; case Hb. Qed.

Lemma equivPif : (Q P) (P Q) if b then Q else ¬ Q.
Proof. by case Hb; auto. Qed.

Lemma xorPif : Q P ¬ (Q P) if b then ¬ Q else Q.
Proof. by case Hb; [intros ? _ H ? | intros ? H _]; case H. Qed.

End ReflectCore.

Internal negated reflection lemmas
Section ReflectNegCore.

Variables (P : Prop) (b : bool) (Hb : reflect P (negb b)) (Q : Prop) (c : bool).

Lemma introTFn : (if c then ¬ P else P) b = c.
Proof. by intro X; apply (introNTF Hb) in X; rewrite <- X; case b. Qed.

Lemma elimTFn : b = c if c then ¬ P else P.
Proof. by intro X; rewrite <- X; apply (elimNTF Hb); case b. Qed.

Lemma equivPifn : (Q P) (P Q) if b then ¬ Q else Q.
Proof. by rewrite <- if_neg; apply equivPif. Qed.

Lemma xorPifn : Q P ¬ (Q P) if b then Q else ¬ Q.
Proof. by rewrite <- if_neg; apply xorPif. Qed.

End ReflectNegCore.

User-oriented reflection lemmas
Section Reflect.

Variables (P Q : Prop) (b b' c : bool).
Hypotheses (Pb : reflect P b) (Pb' : reflect P (negb b')).

Lemma introT : P b.
Proof. by apply (introTF Pb (c:=true)). Qed.
Lemma introF : ¬ P b = false.
Proof. by apply (introTF Pb (c:=false)). Qed.
Lemma introN : ¬ P negb b.
Proof. by apply (introNTF Pb (c:=true)). Qed.
Lemma introNf : P negb b = false.
Proof. by apply (introNTF Pb (c:=false)). Qed.
Lemma introTn : ¬ P b'.
Proof. by apply (introTFn Pb' (c:=true)). Qed.
Lemma introFn : P b' = false.
Proof. by apply (introTFn Pb' (c:=false)). Qed.

Lemma elimT : b P.
Proof. by apply (@elimTF _ _ Pb true). Qed.
Lemma elimF : b = false ¬ P.
Proof. by apply (@elimTF _ _ Pb false). Qed.
Lemma elimN : negb b ¬P.
Proof. by apply (@elimNTF _ _ Pb true). Qed.
Lemma elimNf : negb b = false P.
Proof. by apply (@elimNTF _ _ Pb false). Qed.
Lemma elimTn : b' ¬ P.
Proof. by apply (@elimTFn _ _ Pb' true). Qed.
Lemma elimFn : b' = false P.
Proof. by apply (@elimTFn _ _ Pb' false). Qed.

Lemma introP : (b Q) (negb b ¬ Q) reflect Q b.
Proof. by case b; constructor; auto. Qed.

Lemma iffP : (P Q) (Q P) reflect Q b.
Proof. by case Pb; constructor; auto. Qed.

Lemma appP : reflect Q b P Q.
Proof. by intro Qb; intro X; apply introT in X; revert X; case Qb. Qed.

Lemma sameP : reflect P c b = c.
Proof. intro X; case X; [exact introT | exact introF]. Qed.

Lemma decPcases : if b then P else ¬ P.
Proof. by case Pb. Qed.

Definition decP : {P} + {¬ P}.
Proof. by generalize decPcases; case b; [left | right]. Defined.

End Reflect.

Coercion elimT : reflect >-> Funclass.

Section ReflectConnectives.

Variable b1 b2 b3 b4 b5 : bool.

Lemma idP : reflect b1 b1.
Proof. by case b1; constructor. Qed.

Lemma idPn : reflect (negb b1) (negb b1).
Proof. by case b1; constructor. Qed.

Lemma negP : reflect (¬ b1) (negb b1).
Proof. by case b1; constructor; auto. Qed.

Lemma negPn : reflect b1 (negb (negb b1)).
Proof. by case b1; constructor. Qed.

Lemma negPf : reflect (b1 = false) (negb b1).
Proof. by case b1; constructor. Qed.

Lemma andP : reflect (b1 b2) (b1 && b2).
Proof. by case b1; case b2; constructor; try done; intro X; case X. Qed.

Lemma orP : reflect (b1 b2) (b1 || b2).
Proof. by case b1; case b2; constructor; auto; intro X; case X. Qed.

Lemma nandP : reflect (negb b1 negb b2) (negb (b1 && b2)).
Proof. by case b1; case b2; constructor; auto; intro X; case X; auto. Qed.

Lemma norP : reflect (negb b1 negb b2) (negb (b1 || b2)).
Proof. by case b1; case b2; constructor; auto; intro X; case X; auto. Qed.

End ReflectConnectives.

Equality types


These definitions are ported from ssr-eq.

Inductive phantom (T : Type) (p : T) : Type := Phantom.
Implicit Arguments phantom [].
Implicit Arguments Phantom [].
Definition phant_id T1 T2 v1 v2 := phantom T1 v1 phantom T2 v2.
Definition idfun T := (fun x : Tx).

Module Equality.

Definition axiom T (e : T T bool) := x y, reflect (x = y) (e x y).

Structure mixin_of T := Mixin {op : T T bool; _ : axiom op}.
Notation class_of := mixin_of (only parsing).

Section ClassDef.

Structure type := Pack {sort; _ : class_of sort; _ : Type}.
Local Coercion sort : type >-> Sortclass.
Variables (T : Type) (cT : type).
Definition class cT' := match cT' return class_of cT' with @Pack _ c _c end.

Definition pack c := @Pack T c T.
Definition clone := fun c (_ : cT T) (_ : phant_id (pack c) cT) ⇒ pack c.

End ClassDef.

Module Exports.
Coercion sort : type >-> Sortclass.
Notation eqType := type.
Notation EqMixin := Mixin.
Notation EqType T m := (@pack T m).
Notation "[ 'eqMixin' 'of' T ]" := (class _ : mixin_of T)
  (at level 0, format "[ 'eqMixin' 'of' T ]") : form_scope.
Notation "[ 'eqType' 'of' T 'for' C ]" := (@clone T C _ idfun id)
  (at level 0, format "[ 'eqType' 'of' T 'for' C ]") : form_scope.
Notation "[ 'eqType' 'of' T ]" := (@clone T _ _ id id)
  (at level 0, format "[ 'eqType' 'of' T ]") : form_scope.
End Exports.

End Equality.
Export Equality.Exports.

Definition eq_op T := Equality.op (Equality.class T).
Implicit Arguments eq_op [[T]].

Lemma eqE : T x, eq_op x = Equality.op (Equality.class T) x.
Proof. done. Qed.

Lemma eqP : T, Equality.axiom (@eq_op T).
Proof. by unfold eq_op; destruct T as (? & []). Qed.
Implicit Arguments eqP [T].

Notation "x == y" := (eq_op x y)
  (at level 70, no associativity) : bool_scope.
Notation "x == y :> T" := ((x : T) == (y : T))
  (at level 70, y at next level) : bool_scope.
Notation "x != y" := (negb (x == y))
  (at level 70, no associativity) : bool_scope.
Notation "x != y :> T" := (negb (x == y :> T))
  (at level 70, y at next level) : bool_scope.

Lemma vlib__internal_eqP :
   (T: eqType) (x y : T), reflect (x = y) (x == y).
Proof. apply eqP. Qed.

Lemma neqP : (T: eqType) (x y: T), reflect (x y) (x != y).
Proof. intros; case eqP; constructor; auto. Qed.

Lemma beq_refl : (T : eqType) (x : T), x == x.
Proof. by intros; case eqP. Qed.

Lemma beq_sym : (T : eqType) (x y : T), (x == y) = (y == x).
Proof. intros; do 2 case eqP; congruence. Qed.

Hint Resolve beq_refl : vlib.
Hint Rewrite beq_refl : vlib_trivial.

Notation eqxx := beq_refl.

Basic simplification tactics


Lemma vlib__negb_rewrite : b, negb b b = false.
Proof. by intros []. Qed.

Lemma vlib__andb_split : b1 b2, b1 && b2 b1 b2.
Proof. by intros [] []. Qed.

Lemma vlib__nandb_split : b1 b2, b1 && b2 = false b1 = false b2 = false.
Proof. intros [] []; auto. Qed.

Lemma vlib__orb_split : b1 b2, b1 || b2 b1 b2.
Proof. intros [] []; auto. Qed.

Lemma vlib__norb_split : b1 b2, b1 || b2 = false b1 = false b2 = false.
Proof. intros [] []; auto. Qed.

Lemma vlib__eqb_split : b1 b2 : bool, (b1 b2) (b2 b1) b1 = b2.
Proof. intros [] [] H H'; unfold is_true in *; auto using sym_eq. Qed.

Lemma vlib__beq_rewrite : (T : eqType) (x1 x2 : T), x1 == x2 x1 = x2.
Proof. by intros until 0; case eqP. Qed.

Set up for basic simplification: database of reflection lemmas

Create HintDb vlib_refl discriminated.

Hint Resolve andP orP nandP norP negP vlib__internal_eqP neqP : vlib_refl.

Ltac vlib__complaining_inj f H :=
  let X := fresh in
  (match goal with | [|- ?P ] ⇒ set (X := P) end);
  injection H;
  
  clear H; intros; subst X;
  try subst.

Ltac vlib__clarify1 :=
  try subst;
  repeat match goal with
  | [H: is_true (andb _ _) |- _] ⇒
      let H' := fresh H in case (vlib__andb_split H); clear H; intros H' H
  | [H: is_true (negb ?x) |- _] ⇒ rewrite (vlib__negb_rewrite H) in ×
  | [H: is_true ?x |- _] ⇒ rewrite H in ×
  | [H: ?x = true |- _] ⇒ rewrite H in ×
  | [H: ?x = false |- _] ⇒ rewrite H in ×
  | [H: is_true (_ == _) |- _] ⇒ generalize (vlib__beq_rewrite H); clear H; intro H
  | [H: @existT _ _ _ _ = @existT _ _ _ _ |- _] ⇒ apply inj_pair2 in H; try subst
  | [H: ?f _ = ?f _ |- _] ⇒ vlib__complaining_inj f H
  | [H: ?f _ _ = ?f _ _ |- _] ⇒ vlib__complaining_inj f H
  | [H: ?f _ _ _ = ?f _ _ _ |- _] ⇒ vlib__complaining_inj f H
  | [H: ?f _ _ _ _ = ?f _ _ _ _ |- _] ⇒ vlib__complaining_inj f H
  | [H: ?f _ _ _ _ _ = ?f _ _ _ _ _ |- _] ⇒ vlib__complaining_inj f H
  | [H: ?f _ _ _ _ _ _ = ?f _ _ _ _ _ _ |- _] ⇒ vlib__complaining_inj f H
  | [H: ?f _ _ _ _ _ _ _ = ?f _ _ _ _ _ _ _ |- _] ⇒ vlib__complaining_inj f H
  end; try done.

Perform injections & discriminations on all hypotheses

Ltac clarify :=
  vlib__clarify1;
  repeat match goal with
    | H1: ?x = Some _, H2: ?x = None |- _rewrite H2 in H1; discriminate
    | H1: ?x = Some _, H2: ?x = Some _ |- _rewrite H2 in H1; vlib__clarify1
  end; try done.

Kill simple goals that require up to two econstructor calls.

Ltac vauto :=
  (clarify; try edone;
   try [> econstructor; (solve [edone | [> econstructor; edone]])]).

Check that the hypothesis id is defined. This is useful to make sure that an assert has been completely finished.

Ltac end_assert id :=
  let m := fresh in
  pose (m := refl_equal id); clear m.

Ltac inv x := inversion x; clarify.
Ltac simpls := simpl in *; try done.
Ltac ins := simpl in *; try done; intros.

Tactic Notation "case_eq" constr(x) := case_eq (x).

Tactic Notation "case_eq" constr(x) "as" simple_intropattern(H) :=
  destruct x as [] _eqn: H; try done.

Ltac vlib__clarsimp1 :=
  clarify; (autorewrite with vlib_trivial vlib in × );
  (autorewrite with vlib_trivial in × ); try done;
  clarify; auto 1 with vlib.

Ltac clarsimp := intros; simpl in *; vlib__clarsimp1.

Ltac autos := clarsimp; auto with vlib.

Destruct but give useful names

Definition NW (P: unit Prop) : Prop := P tt.

Notation "<< x : t >>" := (NW (fun xt)) (at level 80, x ident, no associativity).
Notation "<< t >>" := (NW (fun _t)) (at level 79, no associativity).

Ltac unnw := unfold NW in ×.
Ltac rednw := red; unnw.

Hint Unfold NW.

Destruct, but no case split
Ltac desc :=
  repeat match goal with
    | H: is_true (_ == _) |- _generalize (vlib__beq_rewrite H); clear H; intro H
    | H : x, NW (fun y_) |- _
      let x' := fresh x in let y' := fresh y in destruct H as [x' y']; red in y'
    | H : x, ?p |- _
      let x' := fresh x in destruct H as [x' H]
    | H : ?p ?q |- _
      let x' := match p with | NW (fun z_) ⇒ fresh z | _H end in
      let y' := match q with | NW (fun z_) ⇒ fresh z | _fresh H end in
      destruct H as [x' y'];
      match p with | NW _red in x' | _idtac end;
      match q with | NW _red in y' | _idtac end
    | H : is_true (_ && _) |- _
          let H' := fresh H in case (vlib__andb_split H); clear H; intros H H'
    | H : (_ || _) = false |- _
          let H' := fresh H in case (vlib__norb_split H); clear H; intros H H'
    | H : ?x = ?x |- _clear H


  end.

Ltac des :=
  repeat match goal with
    | H: is_true (_ == _) |- _generalize (vlib__beq_rewrite H); clear H; intro H
    | H : x, NW (fun y_) |- _
      let x' := fresh x in let y' := fresh y in destruct H as [x' y']; red in y'
    | H : x, ?p |- _
      let x' := fresh x in destruct H as [x' H]
    | H : ?p ?q |- _
      let x' := match p with | NW (fun z_) ⇒ fresh z | _H end in
      let y' := match q with | NW (fun z_) ⇒ fresh z | _fresh H end in
      destruct H as [x' y'];
      match p with | NW _red in x' | _idtac end;
      match q with | NW _red in y' | _idtac end
    | H : is_true (_ && _) |- _
        let H' := fresh H in case (vlib__andb_split H); clear H; intros H H'
    | H : (_ || _) = false |- _
        let H' := fresh H in case (vlib__norb_split H); clear H; intros H H'
    | H : ?x = ?x |- _clear H

    | H : ?p ?q |- _
      let x' := match p with | NW (fun z_) ⇒ fresh z | _H end in
      let y' := match q with | NW (fun z_) ⇒ fresh z | _fresh H end in
      destruct H as [x' y'];
      match p with | NW _unfold NW at 1 in x'; red in y' | _idtac end;
      match q with | NW _unfold NW at 1 in y'; red in x' | _idtac end
    | H : ?p ?q |- _
      let x' := match p with | NW (fun z_) ⇒ fresh z | _H end in
      let y' := match q with | NW (fun z_) ⇒ fresh z | _H end in
      destruct H as [x' | y'];
      [ match p with | NW _red in x' | _idtac end
      | match q with | NW _red in y' | _idtac end]
    | H : is_true (_ || _) |- _case (vlib__orb_split H); clear H; intro H
    | H : (_ && _) = false |- _case (vlib__nandb_split H); clear H; intro H
  end.

Ltac des_if_asm :=
  clarify;
  repeat
    match goal with
      | H: context[ match ?x with __ end ] |- _
        match (type of x) with
          | { _ } + { _ }destruct x; clarify
          | bool
            let Heq := fresh "Heq" in
            let P := fresh in
            evar(P: Prop);
            assert (Heq: reflect P x) by (subst P; trivial with vlib_refl);
            subst P; destruct Heq as [Heq|Heq]
          | _let Heq := fresh "Heq" in destruct x as [] _eqn: Heq; clarify
        end
    end.

Ltac des_if_goal :=
  clarify;
  repeat
    match goal with
      | |- context[match ?x with __ end] ⇒
        match (type of x) with
          | { _ } + { _ }destruct x; clarify
          | bool
            let Heq := fresh "Heq" in
            let P := fresh in
            evar(P: Prop);
            assert (Heq: reflect P x) by (subst P; trivial with vlib_refl);
            subst P; destruct Heq as [Heq|Heq]
          | _let Heq := fresh "Heq" in destruct x as [] _eqn: Heq; clarify
        end
    end.

Ltac des_if :=
  clarify;
  repeat
    match goal with
      | |- context[match ?x with __ end] ⇒
        match (type of x) with
          | { _ } + { _ }destruct x; clarify
          | bool
            let Heq := fresh "Heq" in
            let P := fresh in
            evar(P: Prop);
            assert (Heq: reflect P x) by (subst P; trivial with vlib_refl);
            subst P; destruct Heq as [Heq|Heq]
          | _let Heq := fresh "Heq" in destruct x as [] _eqn: Heq; clarify
        end
      | H: context[ match ?x with __ end ] |- _
        match (type of x) with
          | { _ } + { _ }destruct x; clarify
          | bool
            let Heq := fresh "Heq" in
            let P := fresh in
            evar(P: Prop);
            assert (Heq: reflect P x) by (subst P; trivial with vlib_refl);
            subst P; destruct Heq as [Heq|Heq]
          | _let Heq := fresh "Heq" in destruct x as [] _eqn: Heq; clarify
        end
    end.

Ltac des_eqrefl :=
  match goal with
    | H: context[match ?X with __ end Logic.eq_refl] |- _
    let EQ := fresh "EQ" in
    let id' := fresh "x" in
    revert H;
    generalize (Logic.eq_refl X); generalize X at 1 3;
    intros id' EQ; destruct id'; intros H
    | |- context[match ?X with __ end Logic.eq_refl] ⇒
    let EQ := fresh "EQ" in
    let id' := fresh "x" in
    generalize (Logic.eq_refl X); generalize X at 1 3;
    intros id' EQ; destruct id'
  end.

Ltac desf_asm := clarify; des; des_if_asm.

Ltac desf := clarify; des; des_if.

Ltac clarassoc := clarsimp; autorewrite with vlib_trivial vlib vlibA in *; try done.

Ltac vlib__hacksimp1 :=
   clarsimp;
   match goal with
     | H: _ |- _solve [rewrite H; clear H; clarsimp
                         |rewrite <- H; clear H; clarsimp]
     | _solve [f_equal; clarsimp]
   end.

Ltac hacksimp :=
   clarsimp;
   try match goal with
   | H: _ |- _solve [rewrite H; clear H; clarsimp
                              |rewrite <- H; clear H; clarsimp]
   | |- context[match ?p with __ end] ⇒ solve [destruct p; vlib__hacksimp1]
   | _solve [f_equal; clarsimp]
   end.

Delineating cases in proofs


Named case tactics (taken from Libtactics)

Tactic Notation "assert_eq" ident(x) constr(v) :=
  let H := fresh in
  assert (x = v) as H by reflexivity;
  clear H.

Tactic Notation "Case_aux" ident(x) constr(name) :=
  first [
    set (x := name); move x at top
  | assert_eq x name
  | fail 1 "because we are working on a different case." ].

Ltac Case name := Case_aux case name.
Ltac SCase name := Case_aux subcase name.
Ltac SSCase name := Case_aux subsubcase name.
Ltac SSSCase name := Case_aux subsubsubcase name.
Ltac SSSSCase name := Case_aux subsubsubsubcase name.

Lightweight case tactics (without names)

Tactic Notation "--" tactic(c) :=
  first [
    assert (WithinCaseM := True); move WithinCaseM at top
  | fail 1 "because we are working on a different case." ]; c.

Tactic Notation "++" tactic(c) :=
  first [
    assert (WithinCaseP := True); move WithinCaseP at top
  | fail 1 "because we are working on a different case." ]; c.

Exploiting a hypothesis


Exploit an assumption (adapted from CompCert).

Ltac exploit x :=
    refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _ _) _)
 || refine ((fun x yy x) (x _ _ _) _)
 || refine ((fun x yy x) (x _ _) _)
 || refine ((fun x yy x) (x _) _).

Induction


Tactic Notation "induction" "[" ident_list(y) "]" ident(x) :=
  first [ try (intros until x); revert y; induction x
        | red; try (intros until x); revert y; induction x ].

Tactic Notation "induction" "[" ident_list(y) "]" ident(x) "[" ident(z) "]" :=
  first [ try (intros until x); revert y; induction x; destruct z
        | red; try (intros until x); revert y; induction x; destruct z ].

Tactic Notation "induction" "[" ident_list(y) "]" ident(x) "[" ident(z) ident (w) "]" :=
  first [ try (intros until x); revert y; induction x; destruct z, w
        | red; try (intros until x); revert y; induction x; destruct z, w ].

Versions with hacksimp

Tactic Notation "induct" ident(x) := induction x; hacksimp.

Tactic Notation "induct" ident(x) "[" ident(z) "]" :=
  induction x; destruct z; hacksimp.

Tactic Notation "induct" ident(x) "[" ident(z) ident(w) "]" :=
  induction x; destruct z, w; hacksimp.

Tactic Notation "induct" "[" ident_list(y) "]" ident(x) :=
  first [ try (intros until x); revert y; induction x; hacksimp
        | red; try (intros until x); revert y; induction x; hacksimp ].

Tactic Notation "induct" "[" ident_list(y) "]" ident(x) "[" ident(z) "]" :=
  first [ try (intros until x); revert y; induction x; destruct z; hacksimp
        | red; try (intros until x); revert y; induction x; destruct z; hacksimp ].

Tactic Notation "induct" "[" ident_list(y) "]" ident(x) "[" ident(z) ident(w) "]" :=
  first [ try (intros until x); revert y; induction x; destruct z, w; hacksimp
        | red; try (intros until x); revert y; induction x; destruct z, w; hacksimp ].

Views


Ltac vlib__apply_refl :=
  intros;
    match goal with
      | |- is_true ?peapply introT; [solve [trivial with vlib_refl]|]
      | |- ?p = trueeapply introT; [solve [trivial with vlib_refl]|]
      | |- ?p = falseeapply introFn; [solve [trivial with vlib_refl]|]
      | |- ?p = falseeapply introF; [solve [trivial with vlib_refl]|]
      | |- _red; vlib__apply_refl
    end.

Tactic Notation "apply/" := vlib__apply_refl.

Tactic Notation "apply/" constr(X) :=
  first [eapply X | eapply elimT; [eapply X; edone|]
    | eapply introT; [eapply X; edone|]
    | eapply introFn; [eapply X; edone|]
    | eapply introF; [eapply X; edone|]].

Tactic Notation "split/" :=
  first [split | hnf; intros; apply/ ; split
        | try red; intros; apply vlib__eqb_split].

apply in assumption

Ltac vlib__apply_refl_in H :=
  first [eapply elimT in H; [|solve [trivial with vlib_refl]]
|eapply elimFn in H; [|solve [trivial with vlib_refl]]
|eapply elimF in H; [|solve [trivial with vlib_refl]]].

Ltac vlib__apply_with_in X H :=
  first [eapply X in H
        |eapply elimT in H; [|eapply X; edone]
        |eapply elimFn in H; [|eapply X; edone]
        |eapply elimF in H; [|eapply X; edone]].

Tactic Notation "apply/" "in" hyp(H) := vlib__apply_refl_in H.

Tactic Notation "apply/" constr(X) "in" hyp(H) := vlib__apply_with_in X H.

double apply

Tactic Notation "apply/" constr(X1) "/" constr(X2) :=
  eapply sameP; [apply X1; edone|eapply iffP; [apply X2; edone|instantiate|instantiate]].

Function notation ported from ssrfun.v


Delimit Scope fun_scope with FUN.
Open Scope fun_scope.

Notation "f ^~ y" := (fun xf x y)
  (at level 10, y at level 8, no associativity, format "f ^~ y") : fun_scope.

Module Option.

Definition apply aT rT (f : aT rT) x u :=
  match u with
    | Some yf y
    | Nonex
  end.

Definition default T := apply (fun x : Tx).

Definition bind aT rT (f : aT option rT) := apply f None.

Definition map aT rT (f : aT rT) := bind (fun xSome (f x)).

End Option.

Notation oapp := Option.apply.
Notation odflt := Option.default.
Notation obind := Option.bind.
Notation omap := Option.map.
Notation some := (@Some _) (only parsing).

Definitions and notation for explicit functions with simplification.

Section SimplFun.

Variables aT rT : Type.

Inductive simpl_fun : Type := SimplFun (_ : aT rT).

Definition fun_of_simpl := fun f xmatch f with SimplFun lamlam x end.

Coercion fun_of_simpl : simpl_fun >-> Funclass.

End SimplFun.

Notation "[ 'fun' : T => E ]" := (SimplFun (fun _ : TE))
  (at level 0,
   format "'[hv' [ 'fun' : T => '/ ' E ] ']'") : fun_scope.

Notation "[ 'fun' x => E ]" := (SimplFun (fun xE))
  (at level 0, x ident,
   format "'[hv' [ 'fun' x => '/ ' E ] ']'") : fun_scope.

Notation "[ 'fun' x : T => E ]" := (SimplFun (fun x : TE))
  (at level 0, x ident, only parsing) : fun_scope.

Notation "[ 'fun' x y => E ]" := (fun x[fun y E])
  (at level 0, x ident, y ident,
   format "'[hv' [ 'fun' x y => '/ ' E ] ']'") : fun_scope.

Notation "[ 'fun' x y : T => E ]" := (fun x : T[fun y : T E])
  (at level 0, x ident, y ident, only parsing) : fun_scope.

Notation "[ 'fun' ( x : T ) y => E ]" := (fun x : T[fun y E])
  (at level 0, x ident, y ident, only parsing) : fun_scope.

Notation "[ 'fun' x ( y : T ) => E ]" := (fun x[fun y : T E])
  (at level 0, x ident, y ident, only parsing) : fun_scope.

Notation "[ 'fun' ( x : xT ) ( y : yT ) => E ]" :=
    (fun x : xT[fun y : yT E])
  (at level 0, x ident, y ident, only parsing) : fun_scope.

Definition erefl := @eq_refl.
Definition esym := eq_sym.
Definition nesym := sym_not_eq.
Definition etrans := eq_trans.
Definition congr1 := f_equal.
Definition congr2 := f_equal2.

A predicate for singleton types.
Definition all_equal_to T (x0 : T) := x, x = x0.

Lemma unitE : all_equal_to tt.
Proof. by intros []. Qed.

A generic wrapper type

Structure wrapped T := Wrap {unwrap : T}.
Canonical Structure wrap T x := @Wrap T x.


Extensional equality for unary and binary functions + syntactic sugar.

Section ExtensionalEquality.

Variables A B C : Type.

Definition eqfun (f g : B A) : Prop := x, f x = g x.

Definition eqrel (r s : C B A) : Prop := x y, r x y = s x y.

Lemma frefl : f, eqfun f f.
Proof. done. Qed.

Lemma fsym : f g, eqfun f g eqfun g f.
Proof. red; done. Qed.

Lemma ftrans : f g h (EQ1: eqfun f g) (EQ2: eqfun g h), eqfun f h.
Proof. by red; intros; rewrite EQ1. Qed.

Lemma rrefl : r, eqrel r r.
Proof. done. Qed.

End ExtensionalEquality.

Hint Resolve frefl rrefl.

Notation "f1 =1 f2" := (eqfun f1 f2)
  (at level 70, no associativity) : fun_scope.
Notation "f1 =1 f2 :> A" := (f1 =1 (f2 : A))
  (at level 70, f2 at next level, A at level 90) : fun_scope.
Notation "f1 =2 f2" := (eqrel f1 f2)
  (at level 70, no associativity) : fun_scope.
Notation "f1 =2 f2 :> A" := (f1 =2 (f2 : A))
  (at level 70, f2 at next level, A at level 90) : fun_scope.

Section Composition.

Variables A B C : Type.

Definition funcomp u (f : B A) (g : C B) x := match u with ttf (g x) end.
Local Notation comp := (funcomp tt).

Definition pcomp (f : B option A) (g : C option B) x := obind f (g x).

Lemma eq_comp : f f' g g', f =1 f' g =1 g' comp f g =1 comp f' g'.
Proof. red; intros; simpl; congruence. Qed.

End Composition.

Notation "[ 'eta' f ]" := (fun xf x)
  (at level 0, format "[ 'eta' f ]") : fun_scope.

Notation id := (fun xx).
Notation "@ 'id' T " := (fun x : Tx)
  (at level 10, T at level 8, only parsing) : fun_scope.

Notation comp := (funcomp tt).
Notation "@ 'comp'" := (fun A B C ⇒ @funcomp A B C tt).
Notation "f1 \o f2" := (comp f1 f2) (at level 50) : fun_scope.

Section Morphism.

Variables (aT rT sT : Type) (f : aT rT).

Definition morphism_1 aF rF := x, f (aF x) = rF (f x).
Definition morphism_2 aOp rOp := x y, f (aOp x y) = rOp (f x) (f y).

End Morphism.

Notation "{ 'morph' f : x / a >-> r }" :=
  (morphism_1 f (fun xa) (fun xr))
  (at level 0, f at level 99, x ident,
   format "{ 'morph' f : x / a >-> r }") : type_scope.

Notation "{ 'morph' f : x / a }" :=
  (morphism_1 f (fun xa) (fun xa))
  (at level 0, f at level 99, x ident,
   format "{ 'morph' f : x / a }") : type_scope.

Notation "{ 'morph' f : x y / a >-> r }" :=
  (morphism_2 f (fun x ya) (fun x yr))
  (at level 0, f at level 99, x ident, y ident,
   format "{ 'morph' f : x y / a >-> r }") : type_scope.

Notation "{ 'morph' f : x y / a }" :=
  (morphism_2 f (fun x ya) (fun x ya))
  (at level 0, f at level 99, x ident, y ident,
   format "{ 'morph' f : x y / a }") : type_scope.

Properties of relations (ported from ssrfun.v)


Section Injections.

Variables (rT aT : Type) (f : aT rT).

Definition injective := x1 x2, f x1 = f x2 x1 = x2.

Definition cancel g := x, g (f x) = x.

Definition pcancel g := x, g (f x) = Some x.

Definition ocancel (g : aT option rT) h := x, oapp h x (g x) = x.

Lemma can_pcan : g, cancel g pcancel (fun ySome (g y)).
Proof. by red; intros; f_equal. Qed.

Lemma pcan_inj : g, pcancel g injective.
Proof. red; intros; apply (congr1 g) in H0; rewrite !H in *; clarify. Qed.

Lemma can_inj : g, cancel g injective.
Proof. eby intros; apply can_pcan in H; eapply pcan_inj. Qed.

Lemma canLR : g x y, cancel g x = f y g x = y.
Proof. intros; clarify. Qed.

Lemma canRL : g x y, cancel g f x = y x = g y.
Proof. intros; clarify. Qed.

End Injections.

Lemma esymK : T x y, cancel (@eq_sym T x y) (@eq_sym T y x).
Proof. by red; destruct x0. Qed.

Lemma etrans_id : T x y (eqxy : x = y :> T),
  eq_trans (eq_refl x) eqxy = eqxy.
Proof. by destruct eqxy. Qed.

Section InjectionsTheory.

Variables (A B C : Type) (f g : B A) (h : C B).

Lemma inj_id : injective (@id A).
Proof. done. Qed.

Lemma inj_can_sym : f', cancel f f' injective f' cancel f' f.
Proof. red; intros; apply H0, H. Qed.

Lemma inj_comp : injective f injective h injective (f \o h).
Proof. by red; simpl; intros; apply H0, H. Qed.

Lemma can_comp : f' h',
  cancel f f' cancel h h' cancel (f \o h) (h' \o f').
Proof. by red; simpl; intros; rewrite H, H0. Qed.

Lemma pcan_pcomp : f' h',
  pcancel f f' pcancel h h' pcancel (f \o h) (pcomp h' f').
Proof. by red; intros; unfold pcomp; simpl; rewrite H; simpl; rewrite H0. Qed.

Lemma eq_inj : injective f f =1 g injective g.
Proof. intros H H0 x y; simpl; rewrite <- !H0; apply H. Qed.

Lemma eq_can : f' g', cancel f f' f =1 g f' =1 g' cancel g g'.
Proof. by red; intros; rewrite <- H0, <- H1. Qed.

Lemma inj_can_eq : f',
  cancel f f' injective f' cancel g f' f =1 g.
Proof. by red; intros; apply H0; rewrite H1. Qed.

End InjectionsTheory.

Section Bijections.

Variables (A B : Type) (f : B A).

Inductive bijective : Prop := Bijective g (_ : cancel f g) (_ : cancel g f).

Hypothesis bijf : bijective.

Lemma bij_inj : injective f.
Proof. eby destruct bijf; eapply can_inj. Qed.

Lemma bij_can_sym : f', cancel f' f cancel f f'.
Proof.
split; intros; [by apply inj_can_sym, bij_inj|].
by destruct bijf; intros x; rewrite <- (H1 x), H.
Qed.

Lemma bij_can_eq : f' f'', cancel f f' cancel f f'' f' =1 f''.
Proof.
  by intros; eapply inj_can_eq, bij_can_sym; [apply bij_can_sym | apply bij_inj |].
Qed.

End Bijections.

Section BijectionsTheory.

Variables (A B C : Type) (f : B A) (h : C B).

Lemma eq_bij : bijective f g, f =1 g bijective g.
Proof. by destruct 1; g; eapply eq_can; eauto. Qed.

Lemma bij_comp : bijective f bijective h bijective (f \o h).
Proof.
intros [f' fK f'K] [h' hK h'K].
by (h' \o f' : _ _); apply can_comp; auto.
Qed.

Lemma bij_can_bij : bijective f f', cancel f f' bijective f'.
Proof. by f; [apply (bij_can_sym H) |]. Qed.

End BijectionsTheory.

Section Involutions.

Variables (A : Type) (f : A A).

Definition involutive := cancel f f.

Hypothesis Hf : involutive.

Lemma inv_inj : injective f.
Proof. eapply can_inj, Hf. Qed.

Lemma inv_bij : bijective f.
Proof. by f. Qed.

End Involutions.

Section OperationProperties.

Variables S T R : Type.

Section SopTisR.
Implicit Type op : S T R.
Definition left_inverse e inv op := x, op (inv x) x = e.
Definition right_inverse e inv op := x, op x (inv x) = e.
End SopTisR.

Section SopTisS.
Implicit Type op : S T S.
Definition right_id e op := x, op x e = x.
Definition left_zero z op := x, op z x = z.
Definition right_commutative op := x y z, op (op x y) z = op (op x z) y.
Definition left_distributive op add :=
   x y z, op (add x y) z = add (op x z) (op y z).
End SopTisS.

Section SopTisT.
Implicit Type op : S T T.
Definition left_id e op := x, op e x = x.
Definition right_zero z op := x, op x z = z.
Definition left_commutative op := x y z, op x (op y z) = op y (op x z).
Definition right_distributive op add :=
   x y z, op x (add y z) = add (op x y) (op x z).
End SopTisT.

Section SopSisT.
Implicit Type op : S S T.
Definition self_inverse e op := x, op x x = e.
Definition commutative op := x y, op x y = op y x.
End SopSisT.

Section SopSisS.
Implicit Type op : S S S.
Definition idempotent op := x, op x x = x.
Definition associative op := x y z, op x (op y z) = op (op x y) z.
End SopSisS.

End OperationProperties.

Boolean laws

Shorter, more systematic names for the boolean connectives laws.

Lemma andTb : x, true && x = x.
Proof. done. Qed.
Lemma andFb : x, false && x = false.
Proof. done. Qed.
Lemma andbT : x, x && true = x.
Proof. by intros []. Qed.
Lemma andbF : x, x && false = false.
Proof. by intros []. Qed.
Lemma andbb : x, x && x = x.
Proof. by intros []. Qed.

Lemma andbC : x y, x && y = y && x.
Proof. by intros[][]. Qed.
Lemma andbA : x y z, x && (y && z) = x && y && z.
Proof. by intros[][][]. Qed.
Lemma andbCA : x y z, x && (y && z) = y && (x && z).
Proof. by intros[][][]. Qed.
Lemma andbAC : x y z, x && y && z = x && z && y.
Proof. by intros[][][]. Qed.

Lemma andbN : b, b && negb b = false.
Proof. by intros[]. Qed.
Lemma andNb : b, negb b && b = false.
Proof. by intros[]. Qed.

Lemma orTb : x, true || x = true.
Proof. done. Qed.
Lemma orFb : x, false || x = x.
Proof. done. Qed.
Lemma orbT : x, x || true = true.
Proof. by intros[]. Qed.
Lemma orbF : x, x || false = x.
Proof. by intros[]. Qed.
Lemma orbb : x, x || x = x.
Proof. by intros[]. Qed.

Lemma orbC : x y, x || y = y || x.
Proof. by intros[][]. Qed.
Lemma orbA : x y z, x || (y || z) = x || y || z.
Proof. by intros[][][]. Qed.
Lemma orbCA : x y z, x || (y || z) = y || (x || z).
Proof. by intros[][][]. Qed.
Lemma orbAC : x y z, x || y || z = x || z || y.
Proof. by intros[][][]. Qed.

Lemma orbN : b, b || negb b = true.
Proof. by intros[]. Qed.
Lemma orNb : b, negb b || b = true.
Proof. by intros[]. Qed.

Lemma andb_orl : x y z, (x || y) && z = x && z || y && z.
Proof. by intros[][][]. Qed.
Lemma andb_orr : x y z, x && (y || z) = x && y || x && z.
Proof. by intros[][][]. Qed.
Lemma orb_andl : x y z, (x && y) || z = (x || z) && (y || z).
Proof. by intros[][][]. Qed.
Lemma orb_andr : x y z, x || (y && z) = (x || y) && (x || z).
Proof. by intros[][][]. Qed.

Pseudo-cancellation -- i.e, absorbtion

Lemma andbK : b1 b2, b1 && b2 || b1 = b1.
Proof. by intros[][]. Qed.
Lemma andKb : b1 b2, b1 || b2 && b1 = b1.
Proof. by intros[][]. Qed.
Lemma orbK : b1 b2, (b1 || b2) && b1 = b1.
Proof. by intros[][]. Qed.
Lemma orKb : b1 b2, b1 && (b2 || b1) = b1.
Proof. by intros[][]. Qed.

Exclusive or -- xorb

Lemma xorFb : x, xorb false x = x.
Proof. by intros[]. Qed.
Lemma xorbF : x, xorb x false = x.
Proof. by intros[]. Qed.
Lemma xorTb : x, xorb true x = negb x.
Proof. by intros[]. Qed.
Lemma xorbT : x, xorb x true = negb x.
Proof. by intros[]. Qed.
Lemma xorbb : x, xorb x x = false.
Proof. by intros[]. Qed.

Lemma xorbC : x y, xorb x y = xorb y x.
Proof. by intros[][]. Qed.
Lemma xorbA : x y z, xorb x (xorb y z) = xorb (xorb x y) z.
Proof. by intros[][][]. Qed.
Lemma xorbCA : x y z, xorb x (xorb y z) = xorb y (xorb x z).
Proof. by intros[][][]. Qed.
Lemma xorbAC : x y z, xorb (xorb x y) z = xorb (xorb x z) y.
Proof. by intros[][][]. Qed.

Lemma xorbN : x y, xorb x (negb y) = negb (xorb x y).
Proof. by intros[][]. Qed.
Lemma xorNb : x y, xorb x (negb y) = negb (xorb x y).
Proof. by intros[][]. Qed.

Lemma andb_xorl : x y z, (xorb x y) && z = xorb (x && z) (y && z).
Proof. by intros[][][]. Qed.
Lemma andb_xorr : x y z, x && (xorb y z) = xorb (x && y) (x && z).
Proof. by intros[][][]. Qed.

Negation

Lemma negb_neg : x, negb (negb x) = x.
Proof. by intros[]. Qed.
Lemma negb_and : x y, negb (x && y) = negb x || negb y.
Proof. by intros[][]. Qed.
Lemma negb_or : x y, negb (x || y) = negb x && negb y.
Proof. by intros[][]. Qed.
Lemma negb_xor : x y, negb (xorb x y) = xorb (negb x) y.
Proof. by intros[][]. Qed.

Automation support


Hint Rewrite
  andTb andFb andbT andbF
  orTb orFb orbT orbF
  : vlib_trivial.

Hint Rewrite
  andbb andbN andNb
  orbb orbN orNb
  andbK andKb orbK orKb
  xorbb xorFb xorbF xorTb xorbT xorbb negb_neg
  : vlib.

Hint Rewrite andbA orbA xorbA : vlibA.

Comparison for nat

Fixpoint eqn_rec (x y: nat) {struct x} :=
   match x, y with
     | O, Otrue
     | S x, S yeqn_rec x y
     | _, _false
   end.

Definition eqn := match tt with tteqn_rec end.

Lemma eqnP: x y, reflect (x = y) (eqn x y).
Proof.
  induction[] x [y]; vauto.
  change (eqn (S x) (S y)) with (eqn x y).
  case IHx; constructor; congruence.
Qed.

Canonical Structure nat_eqMixin := EqMixin eqnP.
Canonical Structure nat_eqType := Eval hnf in EqType nat nat_eqMixin.

Lemma eqnE : eqn = (@eq_op _).
Proof. done. Qed.

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