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

Lemma message_labels_eventually_occur : forall l p, l <> label_silent -> message_enables_label p l -> message_delivered_label p l -> forall s, weak_fairness lb_step_async label_silent s -> lb_step_execution lb_step_async s -> In p (nwPackets (evt_a (hd s))) -> eventually (now (occurred l)) s.