proposition: Lemma post_card_mess : forall (m : Message) (s1 s2 : Site) (b : Bag_of_message), card_mess m (Post_message m b s1 s2 s1 s2) = (card_mess m (b s1 s2) + 1)%Z.
proof: Proof. intros; unfold card_mess in |- *; rewrite post_here; apply input_S_card; trivial. Qed.
imports: counting