unfold CINC in |- *; auto with zfc.
Qed.

(* Specifications: *)
Theorem CINC_sound_left :
forall E E' E'' : Ens, EQC E E' -> CINC E E'' -> CINC E' E''.
Theorem CINC_sound_left :
forall E E' E'' : Ens, EQC E E' -> CINC E E'' -> CINC E' E''.