Proof using.
intros.
find_apply_lem_hyp in_app_iff.
simpl in *; intuition;
find_false; apply in_app_iff; right; apply in_app_iff; auto.
Qed.

(* Specifications: *)
Lemma Lock_delivered_MsgLock :
forall i,
message_delivered_label (mkPacket (Client i) Server Lock) (MsgLock i).