Proof using.
intros.
eapply message_labels_eventually_occur;
eauto using Locked_enables_MsgLocked, Locked_delivered_MsgLocked.
unfold label_silent. simpl. congruence.
Qed.

Lemma MsgLocked_held :
forall s c,
lb_step_execution lb_step_async s ->
now (occurred (MsgLocked c)) s ->
next (fun s => held (nwState (evt_a (hd s)) (Client c)) = true) s.