intros; intro; inversion H.
simpl in H1.
cut (x = y).
intro EQ; rewrite EQ in H2; inversion H2; auto.
rewrite H0 in H1; injection H1; auto.
Qed.

(* Specifications: *)
Lemma NoMACSubChange2 :
forall (s : SFSstate) (u : SUBJECT), ~ MACSubCtrlAttrHaveChanged s s u.