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+(***********************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team    *)
+(* <O___,, *        INRIA-Rocquencourt  &  LRI-CNRS-Orsay              *)
+(*   \VV/  *************************************************************)
+(*    //   *      This file is distributed under the terms of the      *)
+(*         *       GNU Lesser General Public License Version 2.1       *)
+(***********************************************************************)
+
+(* Finite sets library.  
+ * Authors: Pierre Letouzey and Jean-Christophe Filliâtre 
+ * Institution: LRI, CNRS UMR 8623 - Université Paris Sud
+ *              91405 Orsay, France *)
+
+(* $Id: FSetToFiniteSet.v 8876 2006-05-30 13:43:15Z letouzey $ *)
+
+Require Import Ensembles Finite_sets.
+Require Import FSetInterface FSetProperties OrderedTypeEx.
+
+(** * Going from [FSets] with usual equality 
+    to the old [Ensembles] and [Finite_sets] theory. *)
+
+Module S_to_Finite_set (U:UsualOrderedType)(M:S with Module E := U).
+ Module MP:= Properties(M).
+ Import M MP FM Ensembles Finite_sets.
+
+ Definition mkEns : M.t -> Ensemble M.elt := 
+   fun s x => M.In x s.
+
+ Notation " !! " := mkEns.
+
+ Lemma In_In : forall s x, M.In x s <-> In _ (!!s) x.
+ Proof.
+ unfold In; compute; auto.
+ Qed.
+
+ Lemma Subset_Included : forall s s',  s[<=]s'  <-> Included _ (!!s) (!!s').
+ Proof.
+ unfold Subset, Included, In, mkEns; intuition.
+ Qed.
+
+ Notation " a === b " := (Same_set M.elt a b) (at level 70, no associativity).
+
+ Lemma Equal_Same_set : forall s s', s[=]s' <-> !!s === !!s'.
+ Proof.
+ intros.
+ rewrite double_inclusion.
+ unfold Subset, Included, Same_set, In, mkEns; intuition.
+ Qed.
+
+ Lemma empty_Empty_Set : !!M.empty === Empty_set _.
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intro; set_iff; inversion 1.
+ Qed.
+
+ Lemma Empty_Empty_set : forall s, Empty s -> !!s === Empty_set _.
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intros.
+ destruct(H x H0).
+ inversion H0.
+ Qed.
+
+ Lemma singleton_Singleton : forall x, !!(M.singleton x) === Singleton _ x .
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intro; set_iff; inversion 1; try constructor; auto.
+ Qed.
+
+ Lemma union_Union : forall s s', !!(union s s') === Union _ (!!s) (!!s').
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intro; set_iff; inversion 1; [ constructor 1 | constructor 2 | | ]; auto.
+ Qed.
+
+ Lemma inter_Intersection : forall s s', !!(inter s s') === Intersection _ (!!s) (!!s').
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intro; set_iff; inversion 1; try constructor; auto.
+ Qed.
+
+ Lemma add_Add : forall x s, !!(add x s) === Add _ (!!s) x.
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intro; set_iff; inversion 1; unfold E.eq; auto with sets.
+ inversion H0.
+ constructor 2; constructor.
+ constructor 1; auto.
+ Qed.
+
+ Lemma Add_Add : forall x s s', MP.Add x s s' -> !!s' === Add _ (!!s) x.
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intros.
+ red in H; rewrite H in H0.
+ destruct H0.
+ inversion H0.
+ constructor 2; constructor.
+ constructor 1; auto.
+ red in H; rewrite H; unfold E.eq in *.
+ inversion H0; auto.
+ inversion H1; auto.
+ Qed.
+
+ Lemma remove_Subtract : forall x s, !!(remove x s) === Subtract _ (!!s) x.
+ Proof.
+ unfold Same_set, Included, mkEns, In.
+ split; intro; set_iff; inversion 1; unfold E.eq in *; auto with sets.
+ split; auto.
+ swap H1.
+ inversion H2; auto.
+ Qed.
+
+ Lemma mkEns_Finite : forall s, Finite _ (!!s).
+ Proof.
+ intro s; pattern s; apply set_induction; clear s; intros.
+ intros; replace (!!s) with (Empty_set elt); auto with sets.
+ symmetry; apply Extensionality_Ensembles. 
+ apply Empty_Empty_set; auto.
+ replace (!!s') with (Add _ (!!s) x).
+ constructor 2; auto.
+ symmetry; apply Extensionality_Ensembles. 
+ apply Add_Add; auto.
+ Qed.
+
+ Lemma mkEns_cardinal : forall s, cardinal _ (!!s) (M.cardinal s).
+ Proof.
+ intro s; pattern s; apply set_induction; clear s; intros.
+ intros; replace (!!s) with (Empty_set elt); auto with sets.
+ rewrite cardinal_1; auto with sets.
+ symmetry; apply Extensionality_Ensembles. 
+ apply Empty_Empty_set; auto.
+ replace (!!s') with (Add _ (!!s) x).
+ rewrite (cardinal_2 H0 H1); auto with sets. 
+ symmetry; apply Extensionality_Ensembles. 
+ apply Add_Add; auto.
+ Qed.
+
+End S_to_Finite_set.