Proof using.
intros n c s Hstar Hexec Hfair HNth.
apply eventually_next.
pattern s in HNth.
match goal with
| H1 : ?J1 s, H2 : ?J2 s, H3 : ?J3 s |- _ =>
assert ((J1 /\_ J2 /\_ J3) s) by (now unfold and_tl);
eapply weak_until_eventually with (J := (and_tl J1 (and_tl J2 J3)))
end; simpl in *.
2:now unfold and_tl.
3:eauto using eventually_MsgUnlock.
- intros. unfold and_tl in *. intuition.
eapply MsgUnlock_moves_client; eauto.
- apply weak_until_always; eauto using lb_step_execution_invar, always_inv.
apply weak_until_always; eauto using weak_fairness_invar, always_inv.
eauto using clients_only_move_up_in_queue.
Qed.

(* Specifications: *)
Lemma clients_move_way_up_in_queue :
forall n n' c s,
n' <= n ->
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
/\ (S n = 0 -> In (mkPacket Server (Client c) Locked)
(nwPackets (evt_a (hd s))))) ->
eventually (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.