unfold Paire in |- *; simpl in |- *; simple induction 1; intros b; elim b;
simpl in |- *; auto with zfc.
Qed.
Hint Resolve CIN_Paire_left CIN_Paire_right: zfc.
(* Singleton *)

Theorem CIN_Sing : forall E : Ens, CIN E (Sing E).
unfold Sing in |- *; auto with zfc.