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(* 02110-1301 USA                                                     *)
(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
(****************************************************************************)
(*                 The Calculus of Inductive Constructions                  *)
(*                                                                          *)
(*                                Projet Coq                                *)
(*                                                                          *)
(*                     INRIA                        ENS-CNRS                *)
(*              Rocquencourt                        Lyon                    *)
(*                                                                          *)
(*                                Coq V5.10                                 *)
(*                              Nov 25th 1994                               *)
(*                                                                          *)
(****************************************************************************)
(*                               Ensf_dans.v                                *)
(****************************************************************************)
(*              Formal Language Theory                                      *)
(*                                                                          *)
(*              Judicael Courant - Jean-Christophe Filliatre                *)
(*                                                                          *)
(*              Developped in V5.8  June-July 1993                          *)
(*              Ported     to V5.10 October 1994                            *)
(****************************************************************************)
(*                                                                    *)
(*  APPARTENANCE :                                                    *)
(*    On definit le predicat (dans x E) pour un element x et un       *)
(*    ensemble E.                                                     *)
(*                                                                    *)
Inductive dans : Elt -> Ensf -> Prop :=
| dans_add1 : forall (x : Elt) (e : Ensf), dans x (add x e)
| dans_add2 : forall (x y : Elt) (e : Ensf), dans x e -> dans x (add y e).
Hint Resolve dans_add1 dans_add2.
(*  Quelques resultats concernant l'appartenance...  *)
intros x y e H.
simple inversion H.
left.
injection H1.
intros.
apply trans_equal with x0; [ auto | assumption ].
intro.
right.
injection H2.
intros.
rewrite <- H3.
rewrite <- H1.
assumption.
Qed.

Lemma dans_add_contr :
forall (x y : Elt) (e : Ensf), y <> x -> ~ dans x e -> ~ dans x (add y e).