(* Proof of lem_rId_rel_sig                                                *)
elim
(axs_comprehension (fun c : E => exists x : E, c = couple x x)
(cartesien a a) v0); intros; generalize (H0 H);
clear H H0 H1; intros; elim H; clear H; intros; auto with zfc.
Qed.
(* End of proof of lem_rId_rel_sig                                         *)

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(* Le domaine de l'identite est a                                          *)
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Lemma lem_rId_dom : forall a : E, rdom (rId a) a a (lem_rId_rel_sig a) = a.
unfold rdom in |- *; intros; apply axs_extensionnalite; unfold iff in |- *;
split; intros.