Require Export List SetoidList Omega AutoIndTac Computable.

Set Implicit Arguments.

Set Regular Subst Tactic.

Tactic Notation "inv" hyp(A) := inversion A; subst.
Tactic Notation "invc" hyp(A) := inversion A; subst; clear A.
Tactic Notation "invs" hyp(A) := inversion A; subst; clear_trivial_eqs.
Tactic Notation "invcs" hyp(A) := inversion A; subst; clear A; clear_trivial_eqs.

Tactic Notation "dcr" :=
  repeat (
    match goal with
      | H: _ |- _ ⇒ progress (decompose record H); clear H
    end).

Inductive protected (P:Prop) :=
  Protected (p:P) : protected P.

Lemma protect (P:Prop) : P → protected P.
  intros. econstructor. eauto.
Qed.

Lemma unprotect (P:Prop) : protected P → P.
  inversion 1; eauto.
Qed.

Tactic Notation "protect" hyp(H) := apply protect in H.
Tactic Notation "unprotect" hyp(H) := apply unprotect in H.

Ltac invt ty :=
  match goal with
      | h: ty |- _ ⇒ inv h
      | h: ty _ |- _ ⇒ inv h
      | h: ty _ _ |- _ ⇒ inv h
      | h: ty _ _ _ |- _ ⇒ inv h
      | h: ty _ _ _ _ |- _ ⇒ inv h
      | h: ty _ _ _ _ _ |- _ ⇒ inv h
      | h: ty _ _ _ _ _ _ |- _ ⇒ inv h
      | h: ty _ _ _ _ _ _ _ |- _ ⇒ inv h
      | h: ty _ _ _ _ _ _ _ _ |- _ ⇒ inv h
      | h: ty _ _ _ _ _ _ _ _ _ |- _ ⇒ inv h
  end.

Ltac invts ty :=
  match goal with
      | h: ty |- _ ⇒ invs h
      | h: ty _ |- _ ⇒ invs h
      | h: ty _ _ |- _ ⇒ invs h
      | h: ty _ _ _ |- _ ⇒ invs h
      | h: ty _ _ _ _ |- _ ⇒ invs h
      | h: ty _ _ _ _ _ |- _ ⇒ invs h
      | h: ty _ _ _ _ _ _ |- _ ⇒ invs h
      | h: ty _ _ _ _ _ _ _ |- _ ⇒ invs h
      | h: ty _ _ _ _ _ _ _ _ |- _ ⇒ invs h
      | h: ty _ _ _ _ _ _ _ _ _ |- _ ⇒ invs h
  end.

Definition iffT (A B : Type) := ((A → B) × (B → A))%type.

Notation "A <=> B" := (iffT A B) (at level 95, no associativity) : type_scope.

Class Defaulted (V:Type) := {
  default_el : V
}.

Ltac eq e := assert e; eauto; subst; trivial.

Ltac crush := intros; subst; simpl in *; solve [
    eauto
  | contradiction
  | match goal with [H : ?s |- _] ⇒ now(inversion H; eauto) end
  | (constructor; eauto)
  | (constructor 2; eauto)
  | (constructor 3; eauto)
  | intuition
  ].

Tactic Notation "You are here" := fail.

Require Import Basics Containers.Tactics Morphisms Morphisms_Prop.

Lemma bool_extensionality (x y:bool)
  : (x → y) → (y → x) → x = y.
Proof.
  destruct x,y; intros; eauto. destruct H; eapply I. destruct H0; eapply I.
Qed.

Lemma toImpl (A B: Prop)
  : (A → B) → impl A B.
Proof.
  eauto.
Qed.

Ltac bool_to_prop_assumption H :=
  match goal with
    | [ H : context [Is_true (?x && ?y)] |- _ ]
      ⇒ rewrite (toImpl (@andb_prop_elim x y)) in H
    | [ H : context [Is_true (?x || ?y)] |- _ ]
      ⇒ rewrite (toImpl (@orb_prop_elim x y)) in H
    | [ H : Is_true (false) |- _ ] ⇒ inv H
    | [ H : context [not (?t)] |- _ ] ⇒
      match t with
        | context [Is_true (?x && ?y)] ⇒
          rewrite <- (toImpl (@andb_prop_intro x y)) in H
        | context [Is_true (?x || ?y)] ⇒
          rewrite <- (toImpl (@orb_prop_intro x y)) in H
        | context [Is_true (negb ?x)] ⇒
          rewrite <- (toImpl (@negb_prop_intro x)) in H
      end
    | [ H : context [Is_true (negb ?x)] |- _ ]
      ⇒ rewrite (toImpl (@negb_prop_elim x)) in H
    | _ ⇒ fail
  end.

Lemma true_prop_intro
  : Is_true (true) = True.
Proof.
  eauto.
Qed.

Lemma false_prop_intro
  : Is_true (false) = False.
Proof.
  eauto.
Qed.

Ltac bool_to_prop_goal :=
  match goal with
   | [ _ : _ |- context [Is_true (?x && ?y)] ]
     ⇒ rewrite <- (toImpl (@andb_prop_intro x y))
   | [ _ : _ |- context [not (Is_true (?x && ?y))] ]
     ⇒ rewrite (toImpl (@andb_prop_elim x y))
   | [ _ : _ |- context [Is_true (?x || ?y)] ]
     ⇒ rewrite <- (toImpl (@orb_prop_intro x y))
   | [ _ : _ |- context [not (Is_true (?x || ?y))] ]
     ⇒ rewrite (toImpl (@orb_prop_elim x y))
   | [ _ : _ |- context [Is_true (negb ?x)] ]
     ⇒ rewrite <- (toImpl (@negb_prop_intro x))
   | [ _ : _ |- context [Is_true (true)] ]
     ⇒ rewrite true_prop_intro
   | [ _ : _ |- context [Is_true (false)] ]
     ⇒ rewrite false_prop_intro
   | _ ⇒ fail
  end.

Tactic Notation "bool_to_prop" :=
  repeat bool_to_prop_goal.

Tactic Notation "bool_to_prop" "in" hyp (H) :=
  repeat (bool_to_prop_assumption H).

Tactic Notation "bool_to_prop" "in" "*" :=
  repeat (match goal with
    | [ H : _ |- _ ] ⇒ bool_to_prop in H
  end).

Ltac destr_assumption H :=
  repeat match goal with
           | [ H : _ ∧ _ |- _ ] ⇒ destruct H
         end.

Ltac destr :=
  intros; repeat match goal with
                   | |- _ ∧ _ ⇒ split
                 end.

Tactic Notation "destr" "in" hyp(H) :=
  destr_assumption H.

Tactic Notation "destr" "in" "*" :=
  repeat (match goal with
    | [ H : _ |- _ ] ⇒ destr in H
  end).

Tactic Notation "beq_to_prop" :=
  match goal with
    | [ H : ?Q = true |- Is_true ?Q] ⇒ rewrite H; eapply I
    | [ H : Is_true ?Q |- ?Q = true] ⇒ destruct Q; try destruct H; reflexivity
    | [ H : Is_true ?Q, H' : ?Q = false |- _ ] ⇒ rewrite H' in H; destruct H
    | [ H : Is_true ?Q |- not ((?Q) = false) ] ⇒ let X:= fresh "H" in
      intro X; rewrite X in H; destruct H
    | [ H : ?Q = false |- not (Is_true (?Q)) ] ⇒ rewrite H; cbv; trivial
    | [ H : ?Q, H' : not (?Q) |- _ ] ⇒ exfalso; apply H'; apply H
    | [ H : not (?Q = false) |- Is_true (?Q) ] ⇒
      destruct Q; solve [ apply I | exfalso; eapply H; trivial ]
    | |- Is_true true ⇒ eapply I
    | [ H : not (Is_true (?Q)) |- ?Q = false ] ⇒
      destruct Q; solve [ exfalso; eapply H; eapply I | reflexivity ]
  end.

Tactic Notation "cbool" :=
  simpl in *; bool_to_prop in *; destr in *; bool_to_prop; destr; beq_to_prop.

Tactic Notation "orewrite" constr(A) :=
  let X := fresh "OX" in assert A as X by omega; rewrite X; clear X.

Tactic Notation "orewrite" constr(A) "in" hyp(H) :=
  let X := fresh "OX" in assert A as X by omega; rewrite X in H; clear X.

Ltac on_last_hyp tac :=
  match goal with [ H : _ |- _ ] ⇒ first [ tac H | fail 1 ] end.

Ltac revert_until id :=
  on_last_hyp ltac:(fun id' ⇒
    match id' with
      | id ⇒ idtac
      | _ ⇒ revert id' ; revert_until id
    end).

Tactic Notation "simplify" "if" :=
  match goal with
    | [ H : Is_true (?P) |- context [if ?P then _ else _]] ⇒
      let X := fresh in assert (P = true) as X by cbool; rewrite X; clear X
    | [ H : not (Is_true (?P)) |- context [if ?P then _ else _]] ⇒
      let X := fresh in assert (P = false) as X by cbool; rewrite X; clear X
  end.

Tactic Notation "simplify" "if" "in" "*" :=
  match goal with
    | [ H : Is_true (?P), H' : context [if ?P then _ else _] |- _ ] ⇒
      let X := fresh in assert (P = true) as X by cbool; rewrite X in H'; clear X
    | [ H : not (Is_true (?P)), H' : context [if ?P then _ else _] |- _ ] ⇒
      let X := fresh in assert (P = false) as X by cbool; rewrite X in H'; clear X
  end.

Ltac eqassumption :=
  match goal with
    | [ H : ?C ?t |- ?C ?t' ] ⇒
      let X := fresh in
        cut (C t' = C t);
          [ rewrite X; apply H |
            f_equal; try congruence ]
    | [ H : ?C ?t1 ?t2 |- ?C ?t1' ?t2' ] ⇒
      let X := fresh in
        cut (C t1' t2' = C t1 t2);
          [ intros X; rewrite X; apply H |
            f_equal; try congruence ]
    | [ H : ?C ?t1 ?t2 ?t3 |- ?C ?t1' ?t2' ?t3' ] ⇒
      let X := fresh in
        cut (C t1' t2' t3' = C t1 t2 t3);
          [ intros X; rewrite X; apply H |
            f_equal; try congruence ]
    | [ H : ?C ?t1 ?t2 ?t3 ?t4 |- ?C ?t1' ?t2' ?t3' ?t4' ] ⇒
      let X := fresh in
        cut (C t1' t2' t3' t4' = C t1 t2 t3 t4);
          [ intros X; rewrite X; apply H |
            f_equal; try congruence ]
  end.

Definition fresh {X} `{Equivalence X} (x:X) (Y:list X) : Prop :=
  ¬InA R x Y.

Fixpoint unique X `{Equivalence X} (Y:list X) : Prop :=
  match Y with
    | nil ⇒ True
    | cons x Y' ⇒ ¬InA R x Y' ∧ unique Y'
  end.

Lemma unique_decons X (R : relation X) (H : Equivalence R) x L
    : unique (x::L) → unique L.
Proof.
  intros [A B]; eapply B.
Qed.

Hint Resolve unique_decons.

Ltac let_case_eq :=
  match goal with
    | [ H : context [let (_, _) := ?e in _] |- _ ] ⇒
      let a := fresh "a" in let b := fresh "b" in let eq := fresh "eq" in
        case_eq e; intros a b eq; rewrite eq in H
  end.

Ltac let_pair_case_eq :=
  match goal with
    | [ |- context [let (_, _) := ?e in _] ] ⇒ case_eq e; intros
    | [ H : ?x = (?s, ?t) |- _ ] ⇒
      assert (fst x = s) by (rewrite H; eauto);
      assert (snd x = t) by (rewrite H; eauto); clear H
  end.

Ltac simpl_pair_eqs :=
  match goal with
  | [ H : ?P = (?x, ?y) |- _ ] ⇒ assert (fst P = x) by (rewrite H; eauto);
                                assert (snd P = y) by (rewrite H; eauto); clear H
  | [ H : (?x, ?y) = ?P |- _ ] ⇒ assert (fst P = x) by (rewrite <- H; eauto);
                                assert (snd P = y) by (rewrite <- H; eauto); clear H
  end.

Ltac scofix :=
repeat match goal with
           [H : _ |- _] ⇒
           match H with
             | _ ⇒ revert H
           end
       end; cofix; intros.

Lemma modus_ponens P Q
: P → (P → Q) → Q.
tauto.
Defined.

Tactic Notation "exploiT" tactic(tac) :=
  eapply modus_ponens;[ tac | intros].

Ltac exploit H :=
  eapply modus_ponens;
  [
    let H' := fresh "exploitH" in
    pose proof H as H'; hnf in H';
      eapply H'; clear H'
  | intros].

Tactic Notation "exploiT" constr(ty) :=
  match goal with
      | H: ty |- _ ⇒ exploit H
      | H: ty _ |- _ ⇒ exploit H
      | H: ty _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ _ _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ _ _ _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ _ _ _ _ _ |- _ ⇒ exploit H
      | H: ty _ _ _ _ _ _ _ _ _ |- _ ⇒ exploit H
  end.

Ltac exploit2 H H' :=
  eapply modus_ponens;
  [
    let H' := fresh "exploitH" in
    pose proof H as H'; hnf in H';
      eapply H'; clear H'
  | intros H'].

Tactic Notation "exploit" uconstr(X) := exploit X.
Tactic Notation "exploit" uconstr(X) "as" ident(H) := exploit2 X H.

Definition foo A B C := (A → ¬ B ∨ C).

Lemma test (A B C D : Prop) (a:A) (b:B)

: foo A B C
  → (C → D)
  → D.
Proof.
  intros. exploiT foo. eauto. exploit H. eauto. firstorder.
Qed.

Fixpoint iter A n (s:A) (f: A → A) :=
  match n with
  | 0 ⇒ s
  | S n ⇒ iter n (f s) f
  end.

Lemma iter_comm n A (a:A) (f:A → A)
  : iter (S n) a f = f (iter n a f).
Proof.
  general induction n.
  - simpl; eauto.
  - change (iter (S (S n)) a f) with (iter (S n) (f a) f).
    rewrite IHn; eauto.
Qed.

Require Le Arith.Compare_dec.

Instance le_comp (a b: nat) : Computable (lt a b).
eapply Arith.Compare_dec.lt_dec.
Defined.

Hint Extern 20 ⇒ match goal with
                   | [ H: ?a ∧ ?b |- ?b ] ⇒ eapply H
                   | [ H: ?a ∧ ?b |- ?a ] ⇒ eapply H
                 end.

Instance plus_le_morpism
: Proper (Peano.le ==> Peano.le ==> Peano.le) Peano.plus.
Proof.
  unfold Proper, respectful.
  intros. omega.
Qed.

Instance plus_S_morpism
: Proper (Peano.le ==> Peano.le) S.
Proof.
  unfold Proper, respectful.
  intros. omega.
Qed.

Instance le_lt_morph
: Proper (Peano.ge ==> Peano.le ==> impl) Peano.lt.
Proof.
  unfold Proper, respectful, impl; intros; try omega.
Qed.

Instance le_lt_morph'
: Proper (eq ==> Peano.le ==> impl) Peano.lt.
Proof.
  unfold Proper, respectful, flip, impl; intros; try omega.
Qed.

Instance le_lt_morph''
: Proper (Peano.le ==> eq ==> flip impl) Peano.lt.
Proof.
  unfold Proper, respectful, flip, impl; intros; try omega.
Qed.

Lemma length_map_2 X Y Z (L:list X) (L':list Y) (f:Y→Z)
: length L = length L'
  → length L = length (List.map f L').
Proof.
  intros. rewrite map_length; eauto.
Qed.

Lemma length_map_1 X Y Z (L:list Y) (L':list X) (f:Y→Z)
: length L = length L'
  → length (List.map f L) = length L'.
Proof.
  intros. rewrite map_length; eauto.
Qed.

Create HintDb len discriminated.

Hint Resolve length_map_1 length_map_2 : len.

Lemma rev_swap X (L L':list X)
: rev L = L'
  → L = rev L'.
Proof.
  intros. subst. rewrite rev_involutive; eauto.
Qed.

Inductive already_swapped (P:Prop) := AlreadySwapped.
Lemma mark_swapped P : already_swapped P.
Proof.
  constructor.
Qed.

Hint Extern 1000 ⇒
match goal with
  | [ H : already_swapped (?a = ?b) |- ?a = ?b ] ⇒ fail 1
  | [ |- ?a = ?b ] ⇒ eapply eq_sym; pose proof (mark_swapped (a = b))
end : len.

Hint Immediate eq_trans : len.
Hint Immediate eq_sym : len.

Hint Extern 10 ⇒
match goal with
  [ H : ?a = ?b, H': ?b = ?c |- ?c = ?a ] ⇒ eapply eq_sym; eapply (eq_trans H H')
end : len.

Lemma map_length_ass_both X X' Y Y' (L:list X) (L':list Y) (f:X→X') (g:Y→Y')
  : length L = length L'
    → length (List.map f L) = length (List.map g L').
Proof.
  repeat rewrite map_length; eauto.
Qed.

Lemma app_length_ass_both X Y (L1 L2:list X) (L1' L2':list Y)
  : length L1 = length L1'
    → length L2 = length L2'
    → length (L1 ++ L2) = length (L1' ++ L2').
Proof.
  repeat rewrite app_length; eauto.
Qed.

Hint Resolve map_length_ass_both app_length_ass_both | 2 : len.

Lemma app_length_ass X (L:list X) L' k
  : length L + length L' = k
    → length (L ++ L') = k.
Proof.
  intros; subst. rewrite app_length; eauto.
Qed.

Lemma app_length_ass_right X (L:list X) L' k
  : length L + length L' = k
    → k = length (L ++ L').
Proof.
  intros; subst. rewrite app_length; eauto.
Qed.

Lemma map_length_ass X Y (L:list X) (f:X→Y) k
  : length L = k
    → length (List.map f L) = k.
Proof.
  intros; subst. rewrite map_length; eauto.
Qed.

Lemma map_length_ass_right X Y (L:list X) (f:X→Y) k
  : length L = k
    → k = length (List.map f L).
Proof.
  intros; subst. rewrite map_length; eauto.
Qed.

Lemma length_tl X (l:list X)
  : length (tl l) = length l - 1.
Proof.
  destruct l; simpl; eauto; omega.
Qed.

Lemma pair_eta (X Y:Type) (p:X × Y)
  : p = (fst p, snd p).
Proof.
  destruct p; eauto.
Qed.

Hint Resolve map_length_ass app_length_ass | 4 : len.

Notation "❬ L ❭" := (length L) (at level 9, format "'❬' L '❭'").
Notation "f ⊝ L" := (List.map f L) (at level 50, L at level 50, left associativity).
Notation "'tab' s '‖' L '‖'" := (List.map (fun _ ⇒ s) L)
                                 (at level 50, format "'tab' s '‖' L '‖'", s at level 0, L at level 200).

Notation "〔 X 〕" := (list X) (format "'〔' X '〕'") : type_scope.
Notation "؟" := option.

Lemma len_le_app X Y Z (A:list X) (B:list Y) (C D:list Z) n
  : n < length B
    → length A = length (C ++ D)
    → length B = length C
    → n < length A.
Proof.
  intros LE EQ1 EQ2. rewrite EQ1. rewrite app_length. omega.
Qed.

Hint Resolve len_le_app : len.

Lemma map_length_lt_ass_right X Y (L:list X) (f:X→Y) k
  : k < length L
    → k < length (List.map f L).
Proof.
  intros; subst. rewrite map_length; eauto.
Qed.

Hint Resolve map_length_lt_ass_right : len.

Hint Extern 10 ⇒
match goal with
| [ H : length ?A = length ?B, H' : ?n < length ?B |- ?n < length ?A] ⇒
  rewrite H; eapply H'
| [ H : length ?B = length ?A, H' : ?n < length ?B |- ?n < length ?A] ⇒
  rewrite <- H; eapply H'
end : len.

Lemma length_le_plus X Y (A:list X) (B:list Y) k
  : length A = length B
    → length A ≤ length B + k.
Proof.
  omega.
Qed.

Hint Resolve length_le_plus : len.

Instance instance_impl_2 x
  : Proper (impl ==> impl) (impl x).
Proof.
  unfold Proper, respectful, impl. intros.
  eauto.
Qed.

Instance instance_impl_3
  : Proper (impl --> impl ==> impl) impl.
Proof.
  unfold Proper, respectful, impl, flip. intros.
  eauto.
Qed.

Lemma size_induction (X : Type) (f : X → nat) (p: X →Prop) (x : X)
  : (∀ x, (∀ y, f y < f x → p y) → p x) → p x.
Proof.
  intros A. apply A.
  induction (f x); intros y B.
  exfalso; omega.
  apply A. intros z C. apply IHn. omega.
Qed.

Definition size_recursion (X : Type) (f : X → nat) (p: X → Type) (x : X)
  : (∀ x, (∀ y, f y < f x → p y) → p x) → p x.
Proof.
  intros A. apply A.
  induction (f x); intros y B.
  exfalso; destruct (f y); inv B.
  apply A. intros z C. apply IHn. cbv in B,C. cbv.
  inv B. assumption. eapply le_S in C. eapply le_trans; eauto.
Defined.

Ltac simpl_minus :=
  repeat match goal with
  | [ H : context [?n - ?n] |- _ ]
    ⇒ orewrite (n - n = 0) in H
  end.

Hint Extern 5 (Is_true true) ⇒ eapply I.

Instance map_m_eq A B
  : Proper (@pointwise_relation A B eq ==> eq ==> eq) (@List.map A B).
Proof.
  unfold Proper, respectful, pointwise_relation; intros; subst.
  eapply map_ext; eauto.
Qed.

Instance app_m_eq A
  : Proper (eq ==> eq ==> eq) (@app A).
Proof.
  unfold Proper, respectful; intros; subst; eauto.
Qed.

Lemma app_length_le_ass X (L:list X) L' k
  : length L + length L' ≤ k
    → length (L ++ L') ≤ k.
Proof.
  intros; subst. rewrite app_length; eauto.
Qed.

Lemma app_length_le_ass_right X (L:list X) L' k
  : k ≤ length L + length L'
    → k ≤ length (L ++ L').
Proof.
  intros; subst. rewrite app_length; eauto.
Qed.

Lemma map_length_le_ass X Y (L:list X) (f:X→Y) k
  : length L ≤ k
    → length (List.map f L) ≤ k.
Proof.
  intros; subst. rewrite map_length; eauto.
Qed.

Lemma map_length_le_ass_right X Y (L:list X) (f:X→Y) k
  : k ≤ length L
    → k ≤ length (List.map f L).
Proof.
  intros; subst. rewrite map_length; eauto.
Qed.

Hint Resolve app_length_le_ass app_length_le_ass_right map_length_le_ass map_length_le_ass_right
  : len.

Lemma min_idempotent_ass n m k
  : n = k
    → n = m
    → min n m = k.
Proof.
  intros. repeat subst. eapply Nat.min_idempotent.
Qed.

Hint Resolve min_idempotent_ass : len.

Definition impb (a b:bool) : Prop := if a then b else True.

Instance impb_refl : Reflexive impb.
Proof.
  hnf; destruct x; simpl; eauto.
Qed.

Instance impb_trans : Transitive impb.
Proof.
  hnf; intros [] [] []; eauto.
Qed.

Hint Extern 5 (impb ?a ?a') ⇒
progress (first [has_evar a | has_evar a' | reflexivity]).

Hint Extern 5 ⇒
match goal with
  [ H : impb ?a ?b, H' : impb ?b ?c |- impb ?a ?c ] ⇒
  etransitivity; [ eapply H | eapply H' ]
end.

Instance Is_true_impb
  : Proper (impb ==> impl) Is_true.
Proof.
  unfold Proper, respectful; intros.
  destruct x,y; simpl in *; hnf; eauto.
Qed.

Lemma impb_eq (a b:bool)
  : impb a b
    → impb b a
    → a = b.
Proof.
  destruct a, b; simpl; intros; eauto.
  exfalso; eauto.
Qed.

Ltac destr_sig H :=
  match type of H with
  | context [proj1_sig ?x] ⇒ destruct x; simpl in H
  end.

Tactic Notation "destr_sig" :=
  match goal with
  | [ |- context [proj1_sig (proj1_sig ?x)] ] ⇒ destruct x; simpl
  | [ |- context [proj1_sig ?x] ] ⇒ destruct x; simpl
  end.

Lemma minus_zero_eq n
  : n - 0 = n.
Proof.
  omega.
Qed.

Hint Resolve minus_zero_eq.
Hint Resolve min_l min_r : len.

Hint Extern 5 ⇒
match goal with
| [ H : Is_true ?B, EQ : ?A = ?B |- Is_true ?A] ⇒ rewrite EQ; eapply H
| [ H : Is_true ?B, EQ : ?B = ?A |- Is_true ?A] ⇒ rewrite <- EQ; eapply H
end.

Hint Resolve Is_true_eq_true Is_true_eq_left Is_true_eq_right.

Instance ge_computable a b : Computable (a ≥ b).
Proof.
eapply ge_dec.
Qed.