(* Proof of lem_inter_equivClass_empty                                     *)
intros.
apply lem_inter_is_empty; unfold not in |- *; intros.
unfold equivClass in H0; unfold equivClass in H1.
elim (axs_comprehension (fun y : E => In (couple x y) r) a x0); intros;
generalize (H2 H0); clear H0 H2 H3; intros.
elim (axs_comprehension (fun y0 : E => In (couple y y0) r) a x0); intros;
generalize (H2 H1); clear H1 H2 H3; intros.
elim H0; elim H1; clear H0 H1; intros; clear H2.
elim rEqv; clear rEqv; intros.
elim H4; clear H4; unfold symmetry in |- *; unfold transitivity in |- *;
intros.
generalize (H4 y x0 H1); clear H1 H4; intros.
generalize (H5 x x0 y H3 H1); clear H1 H3 H5; intros.
absurd (In (couple x y) r); auto with zfc.
unfold equivClass in H0; unfold equivClass in H1.
elim (axs_comprehension (fun y1 : E => In (couple y y1) r) a y0); intros;
generalize (H2 H0); clear H0 H2 H3; intros.
elim (axs_comprehension (fun y : E => In (couple x y) r) a y0); intros;
generalize (H2 H1); clear H1 H2 H3; intros.
elim H0; elim H1; clear H0 H1; intros; clear H2.
elim rEqv; clear rEqv; unfold symmetry in |- *; unfold transitivity in |- *;
intros; elim H4; clear H4; intros.
generalize (H4 y y0 H3); clear H3 H4; intros.
generalize (H5 x y0 y H1 H3); clear H1 H3 H5; intros.
absurd (In (couple x y) r); auto with zfc.
Qed.
(* End of proof of lem_inter_equivClass_empty                              *)

Lemma lem_equivClass_in_parties_a :
forall (r a : E) (rRel : rel_sig r a a) (rEqv : equivalence r a rRel)
(x : E), In (equivClass r a rRel rEqv x) (parties a).