Definition label_eq_dec :
    forall x y : label,
      {x = y} + {x <> y}.

Lemma messages_trigger_labels : forall l p, message_enables_label p l -> message_delivered_label p l -> forall s, lb_step_execution lb_step_async s -> In p (nwPackets (evt_a (hd s))) -> weak_until (now (enabled lb_step_async l)) (now (occurred l)) s.