elim X1; intros.
elim X2; intros.
elim (a x); intros.
exists x0; apply EQC_tran with (e x); auto with zfc.
Qed.
Hint Resolve EQC_sym EQC_refl EQC_INC: zfc.

Theorem CINC_EQC : forall E E' : Ens, CINC E E' -> CINC E' E -> EQC E E'.
simple induction E; simple induction E'; unfold CINC in |- *; simpl in |- *;
intros; split; intros.