Definition message_delivered_label p l :=
    forall l' net net' tr,
      lb_step_async net l' net' tr ->
      In p (nwPackets net) ->
      ~ In p (nwPackets net') ->
      l = l'.

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