(* Proof of lem_rel_and_rImg2                                              *)
unfold rImg2 in |- *; intros.
elim
(axs_comprehension (fun y0 : E => exists x : E, In (couple x y0) r)
(reunion (reunion r)) y); intros; apply H1; clear H0 H1;
intros.
split; [ idtac | exists x; auto with zfc ].
elim (axs_reunion (reunion r) y); intros; apply H1; clear H0 H1; intros.
exists (paire x y); split;
[ idtac
| elim (axs_paire x y y); intros; apply H1; intros; right; reflexivity ].
elim (axs_reunion r (paire x y)); intros; apply H1; clear H0 H1; intros.
exists (couple x y); split;
[ auto with zfc
| elim (axs_paire (singleton x) (paire x y) (paire x y)); intros; apply H1;
right; reflexivity ].
Qed.
(* End of proof of lem_rel_and_rImg2                                       *)
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(* Relation partielle vs relation totale                                   *)
(* Nous considerons ici qu'une relation est totale si tous les elements de *)
(* son domaine sont "consommes" par la relation.                           *)
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Definition rel_total (r a b : E) (rRel : rel_sig r a b) :=
rdom r a b rRel = a.
Definition rel_partiel (r a b : E) (rRel : rel_sig r a b) :=
exists x : E, In x a -> forall y : E, ~ In (couple x y) r.
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(* Proprietes de base des relations                                        *)
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(* Toute application est une relation                                      *)
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Lemma lem_fun_is_rel : forall (f : E) (Af : fun_ f), rel f.
unfold rel in |- *; intros.