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(* Copyright (c) 2012-2015, Robbert Krebbers. *)
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(* This file is distributed under the terms of the BSD license. *)
(** This file collects definitions and theorems on collections. Most
importantly, it implements some tactics to automatically solve goals involving
collections. *)
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From stdpp Require Export base tactics orders.
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Instance collection_disjoint `{ElemOf A C} : Disjoint C := λ X Y,
   x, x  X  x  Y  False.
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Instance collection_subseteq `{ElemOf A C} : SubsetEq C := λ X Y,
   x, x  X  x  Y.
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Typeclasses Opaque collection_disjoint collection_subseteq.
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(** * Basic theorems *)
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Section simple_collection.
  Context `{SimpleCollection A C}.
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  Implicit Types x y : A.
  Implicit Types X Y : C.
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  Lemma elem_of_empty x : x    False.
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  Proof. split. apply not_elem_of_empty. done. Qed.
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  Lemma elem_of_union_l x X Y : x  X  x  X  Y.
  Proof. intros. apply elem_of_union. auto. Qed.
  Lemma elem_of_union_r x X Y : x  Y  x  X  Y.
  Proof. intros. apply elem_of_union. auto. Qed.
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  Global Instance: EmptySpec C.
  Proof. firstorder auto. Qed.
  Global Instance: JoinSemiLattice C.
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  Proof. firstorder auto. Qed.
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  Global Instance: AntiSymm () (@collection_subseteq A C _).
  Proof. done. Qed.
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  Lemma elem_of_subseteq X Y : X  Y   x, x  X  x  Y.
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  Proof. done. Qed.
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  Lemma elem_of_equiv X Y : X  Y   x, x  X  x  Y.
  Proof. firstorder. Qed.
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  Lemma elem_of_equiv_alt X Y :
    X  Y  ( x, x  X  x  Y)  ( x, x  Y  x  X).
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  Proof. firstorder. Qed.
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  Lemma elem_of_equiv_empty X : X     x, x  X.
  Proof. firstorder. Qed.
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  Lemma elem_of_disjoint X Y : X  Y   x, x  X  x  Y  False.
  Proof. done. Qed.

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  Global Instance disjoint_sym : Symmetric (@disjoint C _).
  Proof. intros ??. rewrite !elem_of_disjoint; naive_solver. Qed.
  Lemma disjoint_empty_l Y :   Y.
  Proof. rewrite elem_of_disjoint; intros x; by rewrite elem_of_empty. Qed.
  Lemma disjoint_empty_r X : X  .
  Proof. rewrite (symmetry_iff _); apply disjoint_empty_l. Qed.
  Lemma disjoint_singleton_l x Y : {[ x ]}  Y  x  Y.
  Proof.
    rewrite elem_of_disjoint; setoid_rewrite elem_of_singleton; naive_solver.
  Qed.
  Lemma disjoint_singleton_r y X : X  {[ y ]}  y  X.
  Proof. rewrite (symmetry_iff ()). apply disjoint_singleton_l. Qed.
  Lemma disjoint_union_l X1 X2 Y : X1  X2  Y  X1  Y  X2  Y.
  Proof.
    rewrite !elem_of_disjoint; setoid_rewrite elem_of_union; naive_solver.
  Qed.
  Lemma disjoint_union_r X Y1 Y2 : X  Y1  Y2  X  Y1  X  Y2.
  Proof. rewrite !(symmetry_iff () X). apply disjoint_union_l. Qed.

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  Lemma collection_positive_l X Y : X  Y    X  .
  Proof.
    rewrite !elem_of_equiv_empty. setoid_rewrite elem_of_union. naive_solver.
  Qed.
  Lemma collection_positive_l_alt X Y : X    X  Y  .
  Proof. eauto using collection_positive_l. Qed.
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  Lemma elem_of_singleton_1 x y : x  {[y]}  x = y.
  Proof. by rewrite elem_of_singleton. Qed.
  Lemma elem_of_singleton_2 x y : x = y  x  {[y]}.
  Proof. by rewrite elem_of_singleton. Qed.
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  Lemma elem_of_subseteq_singleton x X : x  X  {[ x ]}  X.
  Proof.
    split.
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    - intros ??. rewrite elem_of_singleton. by intros ->.
    - intros Ex. by apply (Ex x), elem_of_singleton.
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  Qed.
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  Global Instance singleton_proper : Proper ((=) ==> ()) (singleton (B:=C)).
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  Proof. by repeat intro; subst. Qed.
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  Global Instance elem_of_proper :
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    Proper ((=) ==> () ==> iff) (@elem_of A C _) | 5.
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  Proof. intros ???; subst. firstorder. Qed.
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  Global Instance disjoint_proper: Proper (() ==> () ==> iff) (@disjoint C _).
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  Proof. intros ??????. by rewrite !elem_of_disjoint; setoid_subst. Qed.
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  Lemma elem_of_union_list Xs x : x   Xs   X, X  Xs  x  X.
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  Proof.
    split.
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    - induction Xs; simpl; intros HXs; [by apply elem_of_empty in HXs|].
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      setoid_rewrite elem_of_cons. apply elem_of_union in HXs. naive_solver.
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    - intros [X []]. induction 1; simpl; [by apply elem_of_union_l |].
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      intros. apply elem_of_union_r; auto.
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  Qed.
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  Lemma non_empty_singleton x : ({[ x ]} : C)  .
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  Proof. intros [E _]. by apply (elem_of_empty x), E, elem_of_singleton. Qed.
  Lemma not_elem_of_singleton x y : x  {[ y ]}  x  y.
  Proof. by rewrite elem_of_singleton. Qed.
  Lemma not_elem_of_union x X Y : x  X  Y  x  X  x  Y.
  Proof. rewrite elem_of_union. tauto. Qed.

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  Section leibniz.
    Context `{!LeibnizEquiv C}.
    Lemma elem_of_equiv_L X Y : X = Y   x, x  X  x  Y.
    Proof. unfold_leibniz. apply elem_of_equiv. Qed.
    Lemma elem_of_equiv_alt_L X Y :
      X = Y  ( x, x  X  x  Y)  ( x, x  Y  x  X).
    Proof. unfold_leibniz. apply elem_of_equiv_alt. Qed.
    Lemma elem_of_equiv_empty_L X : X =    x, x  X.
    Proof. unfold_leibniz. apply elem_of_equiv_empty. Qed.
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    Lemma collection_positive_l_L X Y : X  Y =   X = .
    Proof. unfold_leibniz. apply collection_positive_l. Qed.
    Lemma collection_positive_l_alt_L X Y : X    X  Y  .
    Proof. unfold_leibniz. apply collection_positive_l_alt. Qed.
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    Lemma non_empty_singleton_L x : {[ x ]}  .
    Proof. unfold_leibniz. apply non_empty_singleton. Qed.
  End leibniz.
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End simple_collection.

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(** * Tactics *)
(** The tactic [set_unfold] transforms all occurrences of [(∪)], [(∩)], [(∖)],
[(<$>)], [∅], [{[_]}], [(≡)], and [(⊆)] into logically equivalent propositions
involving just [∈]. For example, [A → x ∈ X ∪ ∅] becomes [A → x ∈ X ∨ False].

This transformation is implemented using type classes instead of [rewrite]ing
to ensure that we traverse each term at most once. *)
Class SetUnfold (P Q : Prop) := { set_unfold : P  Q }.
Arguments set_unfold _ _ {_}.
Hint Mode SetUnfold + - : typeclass_instances.

Class SetUnfoldSimpl (P Q : Prop) := { set_unfold_simpl : SetUnfold P Q }.
Hint Extern 0 (SetUnfoldSimpl _ _) => csimpl; constructor : typeclass_instances.

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Instance set_unfold_default P : SetUnfold P P | 1000. done. Qed.
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Definition set_unfold_1 `{SetUnfold P Q} : P  Q := proj1 (set_unfold P Q).
Definition set_unfold_2 `{SetUnfold P Q} : Q  P := proj2 (set_unfold P Q).

Lemma set_unfold_impl P Q P' Q' :
  SetUnfold P P'  SetUnfold Q Q'  SetUnfold (P  Q) (P'  Q').
Proof. constructor. by rewrite (set_unfold P P'), (set_unfold Q Q'). Qed.
Lemma set_unfold_and P Q P' Q' :
  SetUnfold P P'  SetUnfold Q Q'  SetUnfold (P  Q) (P'  Q').
Proof. constructor. by rewrite (set_unfold P P'), (set_unfold Q Q'). Qed.
Lemma set_unfold_or P Q P' Q' :
  SetUnfold P P'  SetUnfold Q Q'  SetUnfold (P  Q) (P'  Q').
Proof. constructor. by rewrite (set_unfold P P'), (set_unfold Q Q'). Qed.
Lemma set_unfold_iff P Q P' Q' :
  SetUnfold P P'  SetUnfold Q Q'  SetUnfold (P  Q) (P'  Q').
Proof. constructor. by rewrite (set_unfold P P'), (set_unfold Q Q'). Qed.
Lemma set_unfold_not P P' : SetUnfold P P'  SetUnfold (¬P) (¬P').
Proof. constructor. by rewrite (set_unfold P P'). Qed.
Lemma set_unfold_forall {A} (P P' : A  Prop) :
  ( x, SetUnfold (P x) (P' x))  SetUnfold ( x, P x) ( x, P' x).
Proof. constructor. naive_solver. Qed.
Lemma set_unfold_exist {A} (P P' : A  Prop) :
  ( x, SetUnfold (P x) (P' x))  SetUnfold ( x, P x) ( x, P' x).
Proof. constructor. naive_solver. Qed.

(* Avoid too eager application of the above instances (and thus too eager
unfolding of type class transparent definitions). *)
Hint Extern 0 (SetUnfold (_  _) _) =>
  class_apply set_unfold_impl : typeclass_instances.
Hint Extern 0 (SetUnfold (_  _) _) =>
  class_apply set_unfold_and : typeclass_instances.
Hint Extern 0 (SetUnfold (_  _) _) =>
  class_apply set_unfold_or : typeclass_instances.
Hint Extern 0 (SetUnfold (_  _) _) =>
  class_apply set_unfold_iff : typeclass_instances.
Hint Extern 0 (SetUnfold (¬ _) _) =>
  class_apply set_unfold_not : typeclass_instances.
Hint Extern 1 (SetUnfold ( _, _) _) =>
  class_apply set_unfold_forall : typeclass_instances.
Hint Extern 0 (SetUnfold ( _, _) _) =>
  class_apply set_unfold_exist : typeclass_instances.

Section set_unfold_simple.
  Context `{SimpleCollection A C}.
  Implicit Types x y : A.
  Implicit Types X Y : C.

  Global Instance set_unfold_empty x : SetUnfold (x  ) False.
  Proof. constructor; apply elem_of_empty. Qed.
  Global Instance set_unfold_singleton x y : SetUnfold (x  {[ y ]}) (x = y).
  Proof. constructor; apply elem_of_singleton. Qed.
  Global Instance set_unfold_union x X Y P Q :
    SetUnfold (x  X) P  SetUnfold (x  Y) Q  SetUnfold (x  X  Y) (P  Q).
  Proof.
    intros ??; constructor.
    by rewrite elem_of_union, (set_unfold (x  X) P), (set_unfold (x  Y) Q).
  Qed.
  Global Instance set_unfold_equiv_same X : SetUnfold (X  X) True | 1.
  Proof. done. Qed.
  Global Instance set_unfold_equiv_empty_l X (P : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  SetUnfold (  X) ( x, ¬P x) | 5.
  Proof.
    intros ?; constructor.
    rewrite (symmetry_iff equiv), elem_of_equiv_empty; naive_solver.
  Qed.
  Global Instance set_unfold_equiv_empty_r (P : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  SetUnfold (X  ) ( x, ¬P x) | 5.
  Proof. constructor. rewrite elem_of_equiv_empty; naive_solver. Qed.
  Global Instance set_unfold_equiv (P Q : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  ( x, SetUnfold (x  Y) (Q x)) 
    SetUnfold (X  Y) ( x, P x  Q x) | 10.
  Proof. constructor. rewrite elem_of_equiv; naive_solver. Qed.
  Global Instance set_unfold_subseteq (P Q : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  ( x, SetUnfold (x  Y) (Q x)) 
    SetUnfold (X  Y) ( x, P x  Q x).
  Proof. constructor. rewrite elem_of_subseteq; naive_solver. Qed.
  Global Instance set_unfold_subset (P Q : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  ( x, SetUnfold (x  Y) (Q x)) 
    SetUnfold (X  Y) (( x, P x  Q x)  ¬∀ x, P x  Q x).
  Proof.
    constructor. rewrite subset_spec, elem_of_subseteq, elem_of_equiv.
    repeat f_equiv; naive_solver.
  Qed.
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  Global Instance set_unfold_disjoint (P Q : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  ( x, SetUnfold (x  Y) (Q x)) 
    SetUnfold (X  Y) ( x, P x  Q x  False).
  Proof. constructor. rewrite elem_of_disjoint. naive_solver. Qed.
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  Context `{!LeibnizEquiv C}.
  Global Instance set_unfold_equiv_same_L X : SetUnfold (X = X) True | 1.
  Proof. done. Qed.
  Global Instance set_unfold_equiv_empty_l_L X (P : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  SetUnfold ( = X) ( x, ¬P x) | 5.
  Proof.
    constructor. rewrite (symmetry_iff eq), elem_of_equiv_empty_L; naive_solver.
  Qed.
  Global Instance set_unfold_equiv_empty_r_L (P : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  SetUnfold (X = ) ( x, ¬P x) | 5.
  Proof. constructor. rewrite elem_of_equiv_empty_L; naive_solver. Qed.
  Global Instance set_unfold_equiv_L (P Q : A  Prop) :
    ( x, SetUnfold (x  X) (P x))  ( x, SetUnfold (x  Y) (Q x)) 
    SetUnfold (X = Y) ( x, P x  Q x) | 10.
  Proof. constructor. rewrite elem_of_equiv_L; naive_solver. Qed.
End set_unfold_simple.

Section set_unfold.
  Context `{Collection A C}.
  Implicit Types x y : A.
  Implicit Types X Y : C.

  Global Instance set_unfold_intersection x X Y P Q :
    SetUnfold (x  X) P  SetUnfold (x  Y) Q  SetUnfold (x  X  Y) (P  Q).
  Proof.
    intros ??; constructor. by rewrite elem_of_intersection,
      (set_unfold (x  X) P), (set_unfold (x  Y) Q).
  Qed.
  Global Instance set_unfold_difference x X Y P Q :
    SetUnfold (x  X) P  SetUnfold (x  Y) Q  SetUnfold (x  X  Y) (P  ¬Q).
  Proof.
    intros ??; constructor. by rewrite elem_of_difference,
      (set_unfold (x  X) P), (set_unfold (x  Y) Q).
  Qed.
End set_unfold.

Section set_unfold_monad.
  Context `{CollectionMonad M} {A : Type}.
  Implicit Types x y : A.

  Global Instance set_unfold_ret x y : SetUnfold (x  mret y) (x = y).
  Proof. constructor; apply elem_of_ret. Qed.
  Global Instance set_unfold_bind {B} (f : A  M B) X (P Q : A  Prop) :
    ( y, SetUnfold (y  X) (P y))  ( y, SetUnfold (x  f y) (Q y)) 
    SetUnfold (x  X = f) ( y, Q y  P y).
  Proof. constructor. rewrite elem_of_bind; naive_solver. Qed.
  Global Instance set_unfold_fmap {B} (f : A  B) X (P : A  Prop) :
    ( y, SetUnfold (y  X) (P y)) 
    SetUnfold (x  f <$> X) ( y, x = f y  P y).
  Proof. constructor. rewrite elem_of_fmap; naive_solver. Qed.
  Global Instance set_unfold_join (X : M (M A)) (P : M A  Prop) :
    ( Y, SetUnfold (Y  X) (P Y))  SetUnfold (x  mjoin X) ( Y, x  Y  P Y).
  Proof. constructor. rewrite elem_of_join; naive_solver. Qed.
End set_unfold_monad.

Ltac set_unfold :=
  let rec unfold_hyps :=
    try match goal with
    | H : _ |- _ =>
       apply set_unfold_1 in H; revert H;
       first [unfold_hyps; intros H | intros H; fail 1]
    end in
  apply set_unfold_2; unfold_hyps; csimpl in *.

(** Since [firstorder] fails or loops on very small goals generated by
[set_solver] already. We use the [naive_solver] tactic as a substitute.
This tactic either fails or proves the goal. *)
Tactic Notation "set_solver" "by" tactic3(tac) :=
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  try fast_done;
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  intros; setoid_subst;
  set_unfold;
  intros; setoid_subst;
  try match goal with |- _  _ => apply dec_stable end;
  naive_solver tac.
Tactic Notation "set_solver" "-" hyp_list(Hs) "by" tactic3(tac) :=
  clear Hs; set_solver by tac.
Tactic Notation "set_solver" "+" hyp_list(Hs) "by" tactic3(tac) :=
  clear -Hs; set_solver by tac.
Tactic Notation "set_solver" := set_solver by idtac.
Tactic Notation "set_solver" "-" hyp_list(Hs) := clear Hs; set_solver.
Tactic Notation "set_solver" "+" hyp_list(Hs) := clear -Hs; set_solver.

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Hint Extern 1000 (_  _) => set_solver : set_solver.
Hint Extern 1000 (_  _) => set_solver : set_solver.
Hint Extern 1000 (_  _) => set_solver : set_solver.

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(** * Conversion of option and list *)
Definition of_option `{Singleton A C, Empty C} (mx : option A) : C :=
  match mx with None =>  | Some x => {[ x ]} end.
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Fixpoint of_list `{Singleton A C, Empty C, Union C} (l : list A) : C :=
  match l with [] =>  | x :: l => {[ x ]}  of_list l end.
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Section of_option_list.
  Context `{SimpleCollection A C}.
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  Lemma elem_of_of_option (x : A) mx: x  of_option mx  mx = Some x.
  Proof. destruct mx; set_solver. Qed.
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  Lemma elem_of_of_list (x : A) l : x  of_list l  x  l.
  Proof.
    split.
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    - induction l; simpl; [by rewrite elem_of_empty|].
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      rewrite elem_of_union,elem_of_singleton; intros [->|?]; constructor; auto.
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    - induction 1; simpl; rewrite elem_of_union, elem_of_singleton; auto.
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  Qed.
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  Global Instance set_unfold_of_option (mx : option A) x :
    SetUnfold (x  of_option mx) (mx = Some x).
  Proof. constructor; apply elem_of_of_option. Qed.
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  Global Instance set_unfold_of_list (l : list A) x P :
    SetUnfold (x  l) P  SetUnfold (x  of_list l) P.
  Proof. constructor. by rewrite elem_of_of_list, (set_unfold (x  l) P). Qed.
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End of_option_list.
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Section list_unfold.
  Context {A : Type}.
  Implicit Types x : A.
  Implicit Types l : list A.

  Global Instance set_unfold_nil x : SetUnfold (x  []) False.
  Proof. constructor; apply elem_of_nil. Qed.
  Global Instance set_unfold_cons x y l P :
    SetUnfold (x  l) P  SetUnfold (x  y :: l) (x = y  P).
  Proof. constructor. by rewrite elem_of_cons, (set_unfold (x  l) P). Qed.
  Global Instance set_unfold_app x l k P Q :
    SetUnfold (x  l) P  SetUnfold (x  k) Q  SetUnfold (x  l ++ k) (P  Q).
  Proof.
    intros ??; constructor.
    by rewrite elem_of_app, (set_unfold (x  l) P), (set_unfold (x  k) Q).
  Qed.
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  Global Instance set_unfold_included l k (P Q : A  Prop) :
    ( x, SetUnfold (x  l) (P x))  ( x, SetUnfold (x  k) (Q x)) 
    SetUnfold (l `included` k) ( x, P x  Q x).
  Proof. by constructor; unfold included; set_unfold. Qed.
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End list_unfold.

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(** * Guard *)
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Global Instance collection_guard `{CollectionMonad M} : MGuard M :=
  λ P dec A x, match dec with left H => x H | _ =>  end.
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Section collection_monad_base.
  Context `{CollectionMonad M}.
  Lemma elem_of_guard `{Decision P} {A} (x : A) (X : M A) :
    x  guard P; X  P  x  X.
  Proof.
    unfold mguard, collection_guard; simpl; case_match;
      rewrite ?elem_of_empty; naive_solver.
  Qed.
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  Lemma elem_of_guard_2 `{Decision P} {A} (x : A) (X : M A) :
    P  x  X  x  guard P; X.
  Proof. by rewrite elem_of_guard. Qed.
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  Lemma guard_empty `{Decision P} {A} (X : M A) : guard P; X    ¬P  X  .
  Proof.
    rewrite !elem_of_equiv_empty; setoid_rewrite elem_of_guard.
    destruct (decide P); naive_solver.
  Qed.
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  Global Instance set_unfold_guard `{Decision P} {A} (x : A) X Q :
    SetUnfold (x  X) Q  SetUnfold (x  guard P; X) (P  Q).
  Proof. constructor. by rewrite elem_of_guard, (set_unfold (x  X) Q). Qed.
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  Lemma bind_empty {A B} (f : A  M B) X :
    X = f    X     x, x  X  f x  .
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  Proof. set_solver. Qed.
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End collection_monad_base.
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(** * More theorems *)
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Section collection.
  Context `{Collection A C}.
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  Implicit Types X Y : C.
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  Global Instance: Lattice C.
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  Proof. split. apply _. firstorder auto. set_solver. Qed.
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  Global Instance difference_proper :
     Proper (() ==> () ==> ()) (@difference C _).
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  Proof.
    intros X1 X2 HX Y1 Y2 HY; apply elem_of_equiv; intros x.
    by rewrite !elem_of_difference, HX, HY.
  Qed.
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  Lemma non_empty_inhabited x X : x  X  X  .
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  Proof. set_solver. Qed.
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  Lemma intersection_singletons x : ({[x]} : C)  {[x]}  {[x]}.
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  Proof. set_solver. Qed.
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  Lemma difference_twice X Y : (X  Y)  Y  X  Y.
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  Proof. set_solver. Qed.
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  Lemma subseteq_empty_difference X Y : X  Y  X  Y  .
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  Proof. set_solver. Qed.
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  Lemma difference_diag X : X  X  .
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  Proof. set_solver. Qed.
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  Lemma difference_union_distr_l X Y Z : (X  Y)  Z  X  Z  Y  Z.
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  Proof. set_solver. Qed.
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  Lemma difference_union_distr_r X Y Z : Z  (X  Y)  (Z  X)  (Z  Y).
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  Proof. set_solver. Qed.
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  Lemma difference_intersection_distr_l X Y Z : (X  Y)  Z  X  Z  Y  Z.
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  Proof. set_solver. Qed.
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  Lemma difference_disjoint X Y : X  Y  X  Y  X.
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  Proof. set_solver. Qed.
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  Section leibniz.
    Context `{!LeibnizEquiv C}.
    Lemma intersection_singletons_L x : {[x]}  {[x]} = {[x]}.
    Proof. unfold_leibniz. apply intersection_singletons. Qed.
    Lemma difference_twice_L X Y : (X  Y)  Y = X  Y.
    Proof. unfold_leibniz. apply difference_twice. Qed.
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    Lemma subseteq_empty_difference_L X Y : X  Y  X  Y = .
    Proof. unfold_leibniz. apply subseteq_empty_difference. Qed.
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    Lemma difference_diag_L X : X  X = .
    Proof. unfold_leibniz. apply difference_diag. Qed.
    Lemma difference_union_distr_l_L X Y Z : (X  Y)  Z = X  Z  Y  Z.
    Proof. unfold_leibniz. apply difference_union_distr_l. Qed.
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    Lemma difference_union_distr_r_L X Y Z : Z  (X  Y) = (Z  X)  (Z  Y).
    Proof. unfold_leibniz. apply difference_union_distr_r. Qed.
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    Lemma difference_intersection_distr_l_L X Y Z :
      (X  Y)  Z = X  Z  Y  Z.
    Proof. unfold_leibniz. apply difference_intersection_distr_l. Qed.
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    Lemma difference_disjoint_L X Y : X  Y  X  Y = X.
    Proof. unfold_leibniz. apply difference_disjoint. Qed.
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  End leibniz.

  Section dec.
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    Context `{ (x : A) (X : C), Decision (x  X)}.
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    Lemma not_elem_of_intersection x X Y : x  X  Y  x  X  x  Y.
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    Proof. rewrite elem_of_intersection. destruct (decide (x  X)); tauto. Qed.
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    Lemma not_elem_of_difference x X Y : x  X  Y  x  X  x  Y.
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    Proof. rewrite elem_of_difference. destruct (decide (x  Y)); tauto. Qed.
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    Lemma union_difference X Y : X  Y  Y  X  Y  X.
    Proof.
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      split; intros x; rewrite !elem_of_union, elem_of_difference; [|intuition].
      destruct (decide (x  X)); intuition.
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    Qed.
    Lemma non_empty_difference X Y : X  Y  Y  X  .
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    Proof. intros [HXY1 HXY2] Hdiff. destruct HXY2. set_solver. Qed.
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    Lemma empty_difference_subseteq X Y : X  Y    X  Y.
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    Proof. set_solver. Qed.
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    Context `{!LeibnizEquiv C}.
    Lemma union_difference_L X Y : X  Y  Y = X  Y  X.
    Proof. unfold_leibniz. apply union_difference. Qed.
    Lemma non_empty_difference_L X Y : X  Y  Y  X  .
    Proof. unfold_leibniz. apply non_empty_difference. Qed.
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    Lemma empty_difference_subseteq_L X Y : X  Y =   X  Y.
    Proof. unfold_leibniz. apply empty_difference_subseteq. Qed.
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  End dec.
End collection.

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(** * Quantifiers *)
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Section quantifiers.
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  Context `{SimpleCollection A B} (P : A  Prop).
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  Definition set_Forall X :=  x, x  X  P x.
  Definition set_Exists X :=  x, x  X  P x.

  Lemma set_Forall_empty : set_Forall .
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  Proof. unfold set_Forall. set_solver. Qed.
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  Lemma set_Forall_singleton x : set_Forall {[ x ]}  P x.
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  Proof. unfold set_Forall. set_solver. Qed.
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  Lemma set_Forall_union X Y : set_Forall X  set_Forall Y  set_Forall (X  Y).
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  Proof. unfold set_Forall. set_solver. Qed.
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  Lemma set_Forall_union_inv_1 X Y : set_Forall (X  Y)  set_Forall X.
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  Proof. unfold set_Forall. set_solver. Qed.
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  Lemma set_Forall_union_inv_2 X Y : set_Forall (X  Y)  set_Forall Y.
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  Proof. unfold set_Forall. set_solver. Qed.
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  Lemma set_Exists_empty : ¬set_Exists .
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  Proof. unfold set_Exists. set_solver. Qed.
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  Lemma set_Exists_singleton x : set_Exists {[ x ]}  P x.
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  Proof. unfold set_Exists. set_solver. Qed.
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  Lemma set_Exists_union_1 X Y : set_Exists X  set_Exists (X  Y).
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  Proof. unfold set_Exists. set_solver. Qed.
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  Lemma set_Exists_union_2 X Y : set_Exists Y  set_Exists (X  Y).
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  Proof. unfold set_Exists. set_solver. Qed.
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  Lemma set_Exists_union_inv X Y :
    set_Exists (X  Y)  set_Exists X  set_Exists Y.
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  Proof. unfold set_Exists. set_solver. Qed.
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End quantifiers.

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Section more_quantifiers.
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  Context `{SimpleCollection A B}.
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  Lemma set_Forall_weaken (P Q : A  Prop) (Hweaken :  x, P x  Q x) X :
    set_Forall P X  set_Forall Q X.
  Proof. unfold set_Forall. naive_solver. Qed.
  Lemma set_Exists_weaken (P Q : A  Prop) (Hweaken :  x, P x  Q x) X :
    set_Exists P X  set_Exists Q X.
  Proof. unfold set_Exists. naive_solver. Qed.
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End more_quantifiers.

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(** * Fresh elements *)
(** We collect some properties on the [fresh] operation. In particular we
generalize [fresh] to generate lists of fresh elements. *)
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Fixpoint fresh_list `{Fresh A C, Union C, Singleton A C}
    (n : nat) (X : C) : list A :=
  match n with
  | 0 => []
  | S n => let x := fresh X in x :: fresh_list n ({[ x ]}  X)
  end.
Inductive Forall_fresh `{ElemOf A C} (X : C) : list A  Prop :=
  | Forall_fresh_nil : Forall_fresh X []
  | Forall_fresh_cons x xs :
     x  xs  x  X  Forall_fresh X xs  Forall_fresh X (x :: xs).
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Section fresh.
  Context `{FreshSpec A C}.
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  Implicit Types X Y : C.
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  Global Instance fresh_proper: Proper (() ==> (=)) (fresh (C:=C)).
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  Proof. intros ???. by apply fresh_proper_alt, elem_of_equiv. Qed.
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  Global Instance fresh_list_proper:
    Proper ((=) ==> () ==> (=)) (fresh_list (C:=C)).
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  Proof.
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    intros ? n ->. induction n as [|n IH]; intros ?? E; f_equal/=; [by rewrite E|].
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    apply IH. by rewrite E.
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  Qed.
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  Lemma Forall_fresh_NoDup X xs : Forall_fresh X xs  NoDup xs.
  Proof. induction 1; by constructor. Qed.
  Lemma Forall_fresh_elem_of X xs x : Forall_fresh X xs  x  xs  x  X.
  Proof.
    intros HX; revert x; rewrite <-Forall_forall.
    by induction HX; constructor.
  Qed.
  Lemma Forall_fresh_alt X xs :
    Forall_fresh X xs  NoDup xs   x, x  xs  x  X.
  Proof.
    split; eauto using Forall_fresh_NoDup, Forall_fresh_elem_of.
    rewrite <-Forall_forall.
    intros [Hxs Hxs']. induction Hxs; decompose_Forall_hyps; constructor; auto.
  Qed.
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  Lemma Forall_fresh_subseteq X Y xs :
    Forall_fresh X xs  Y  X  Forall_fresh Y xs.
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  Proof. rewrite !Forall_fresh_alt; set_solver. Qed.
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  Lemma fresh_list_length n X : length (fresh_list n X) = n.
  Proof. revert X. induction n; simpl; auto. Qed.
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  Lemma fresh_list_is_fresh n X x : x  fresh_list n X  x  X.
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  Proof.
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    revert X. induction n as [|n IH]; intros X; simpl;[by rewrite elem_of_nil|].
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    rewrite elem_of_cons; intros [->| Hin]; [apply is_fresh|].
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    apply IH in Hin; set_solver.
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  Qed.
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  Lemma NoDup_fresh_list n X : NoDup (fresh_list n X).
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  Proof.
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    revert X. induction n; simpl; constructor; auto.
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    intros Hin; apply fresh_list_is_fresh in Hin; set_solver.
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  Qed.
  Lemma Forall_fresh_list X n : Forall_fresh X (fresh_list n X).
  Proof.
    rewrite Forall_fresh_alt; eauto using NoDup_fresh_list, fresh_list_is_fresh.
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  Qed.
End fresh.
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(** * Properties of implementations of collections that form a monad *)
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Section collection_monad.
  Context `{CollectionMonad M}.

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  Global Instance collection_fmap_mono {A B} :
    Proper (pointwise_relation _ (=) ==> () ==> ()) (@fmap M _ A B).
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  Proof. intros f g ? X Y ?; set_solver by eauto. Qed.
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  Global Instance collection_fmap_proper {A B} :
    Proper (pointwise_relation _ (=) ==> () ==> ()) (@fmap M _ A B).
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  Proof. intros f g ? X Y [??]; split; set_solver by eauto. Qed.
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  Global Instance collection_bind_mono {A B} :
    Proper (((=) ==> ()) ==> () ==> ()) (@mbind M _ A B).
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  Proof. unfold respectful; intros f g Hfg X Y ?; set_solver. Qed.
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  Global Instance collection_bind_proper {A B} :
    Proper (((=) ==> ()) ==> () ==> ()) (@mbind M _ A B).
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  Proof. unfold respectful; intros f g Hfg X Y [??]; split; set_solver. Qed.
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  Global Instance collection_join_mono {A} :
    Proper (() ==> ()) (@mjoin M _ A).
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  Proof. intros X Y ?; set_solver. Qed.
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  Global Instance collection_join_proper {A} :
    Proper (() ==> ()) (@mjoin M _ A).
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  Proof. intros X Y [??]; split; set_solver. Qed.
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  Lemma collection_bind_singleton {A B} (f : A  M B) x : {[ x ]} = f  f x.
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  Proof. set_solver. Qed.
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  Lemma collection_guard_True {A} `{Decision P} (X : M A) : P  guard P; X  X.
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  Proof. set_solver. Qed.
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  Lemma collection_fmap_compose {A B C} (f : A  B) (g : B  C) (X : M A) :
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    g  f <$> X  g <$> (f <$> X).
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  Proof. set_solver. Qed.
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  Lemma elem_of_fmap_1 {A B} (f : A  B) (X : M A) (y : B) :
    y  f <$> X   x, y = f x  x  X.
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  Proof. set_solver. Qed.
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  Lemma elem_of_fmap_2 {A B} (f : A  B) (X : M A) (x : A) :
    x  X  f x  f <$> X.
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  Proof. set_solver. Qed.
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  Lemma elem_of_fmap_2_alt {A B} (f : A  B) (X : M A) (x : A) (y : B) :
    x  X  y = f x  y  f <$> X.
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  Proof. set_solver. Qed.
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  Lemma elem_of_mapM {A B} (f : A  M B) l k :
    l  mapM f k  Forall2 (λ x y, x  f y) l k.
  Proof.
    split.
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    - revert l. induction k; set_solver by eauto.
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    - induction 1; set_solver.
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  Qed.
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  Lemma collection_mapM_length {A B} (f : A  M B) l k :
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    l  mapM f k  length l = length k.
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  Proof. revert l; induction k; set_solver by eauto. Qed.
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  Lemma elem_of_mapM_fmap {A B} (f : A  B) (g : B  M A) l k :
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    Forall (λ x,  y, y  g x  f y = x) l  k  mapM g l  fmap f k = l.
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  Proof. intros Hl. revert k. induction Hl; set_solver. Qed.
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  Lemma elem_of_mapM_Forall {A B} (f : A  M B) (P : B  Prop) l k :
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    l  mapM f k  Forall (λ x,  y, y  f x  P y) k  Forall P l.
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  Proof. rewrite elem_of_mapM. apply Forall2_Forall_l. Qed.
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  Lemma elem_of_mapM_Forall2_l {A B C} (f : A  M B) (P: B  C  Prop) l1 l2 k :
    l1  mapM f k  Forall2 (λ x y,  z, z  f x  P z y) k l2 
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    Forall2 P l1 l2.
  Proof.
    rewrite elem_of_mapM. intros Hl1. revert l2.
    induction Hl1; inversion_clear 1; constructor; auto.
  Qed.
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End collection_monad.
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(** Finite collections *)
Definition set_finite `{ElemOf A B} (X : B) :=  l : list A,  x, x  X  x  l.

Section finite.
  Context `{SimpleCollection A B}.
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  Global Instance set_finite_subseteq :
     Proper (flip () ==> impl) (@set_finite A B _).
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  Proof. intros X Y HX [l Hl]; exists l; set_solver. Qed.
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  Global Instance set_finite_proper : Proper (() ==> iff) (@set_finite A B _).
  Proof. by intros X Y [??]; split; apply set_finite_subseteq. Qed.
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  Lemma empty_finite : set_finite .
  Proof. by exists []; intros ?; rewrite elem_of_empty. Qed.
  Lemma singleton_finite (x : A) : set_finite {[ x ]}.
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  Proof. exists [x]; intros y ->%elem_of_singleton; left. Qed.
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  Lemma union_finite X Y : set_finite X  set_finite Y  set_finite (X  Y).
  Proof.
    intros [lX ?] [lY ?]; exists (lX ++ lY); intros x.
    rewrite elem_of_union, elem_of_app; naive_solver.
  Qed.
  Lemma union_finite_inv_l X Y : set_finite (X  Y)  set_finite X.
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  Proof. intros [l ?]; exists l; set_solver. Qed.
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  Lemma union_finite_inv_r X Y : set_finite (X  Y)  set_finite Y.
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  Proof. intros [l ?]; exists l; set_solver. Qed.
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End finite.

Section more_finite.
  Context `{Collection A B}.
  Lemma intersection_finite_l X Y : set_finite X  set_finite (X  Y).
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  Proof. intros [l ?]; exists l; intros x [??]%elem_of_intersection; auto. Qed.
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  Lemma intersection_finite_r X Y : set_finite Y  set_finite (X  Y).
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  Proof. intros [l ?]; exists l; intros x [??]%elem_of_intersection; auto. Qed.
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  Lemma difference_finite X Y : set_finite X  set_finite (X  Y).
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  Proof. intros [l ?]; exists l; intros x [??]%elem_of_difference; auto. Qed.
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  Lemma difference_finite_inv X Y `{ x, Decision (x  Y)} :
    set_finite Y  set_finite (X  Y)  set_finite X.
  Proof.
    intros [l ?] [k ?]; exists (l ++ k).
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    intros x ?; destruct (decide (x  Y)); rewrite elem_of_app; set_solver.
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  Qed.
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End more_finite.