Ltac coinductive_case CIH :=
    apply W_tl; simpl in *; auto;
    apply CIH; simpl in *; auto.

Lemma eventually_Unlock : forall n c s, event_step_star step_async step_async_init (hd s) -> lb_step_execution lb_step_async s -> weak_fairness lb_step_async label_silent s -> Nth (queue (nwState (evt_a (hd s)) Server)) (S n) c -> exists c, eventually (fun s => In (mkPacket c Server Unlock) (nwPackets (evt_a (hd s)))) s.