(* Preuve de lem_reunion_unique                                            *)
intros.
generalize (axs_reunion v0); intros.
apply axs_extensionnalite; intros.
generalize (H v2); clear H; unfold iff in |- *; intros.
elim H; clear H; intros.
generalize (H0 v2); clear H0; unfold iff in |- *; intros.
elim H0; clear H0; intros.
split; intros.
clear H0; clear H1; auto with zfc.
clear H; clear H2; auto with zfc.
Qed.
(* Fin de la preuve de lem_reunion_unique                                  *)
(* Autre version                                                           *)
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(* Notion d'union de deux ensembles                                        *)
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Definition union (a b : E) := reunion (paire a b).
Hint Unfold union: zfc.

(* Specifications: *)
Lemma lem_union_propertie :
forall a b v0 : E, In v0 (union a b) <-> In v0 a \/ In v0 b.