(* Proof of lem_vide_application                                           *)
unfold Vide in H; elim (lem_vide_propertie (couple x y) var_vide);
auto with zfc.
Qed.
(* End of proof of lem_vide_application                                    *)

(***************************************************************************)
(* Le domaine de l'application Vide est Vide                               *)
(***************************************************************************)
Lemma lem_dom_vide : dom Vide = Vide.
apply axs_extensionnalite; intros; unfold iff in |- *; split; intros;
unfold dom in H.