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

Lemma MsgUnlock_moves_client : forall n c s, lb_step_execution lb_step_async s -> Nth (queue (nwState (evt_a (hd s)) Server)) (S n) c -> now (occurred MsgUnlock) s -> next (fun s => Nth (queue (nwState (evt_a (hd s)) Server)) n c /\ (n = 0 -> In (mkPacket Server (Client c) Locked) (nwPackets (evt_a (hd s))))) s.