Section MESS_ALT.
(* consequence sur la structure alternee *)
Variable b0 : Bag_of_Data Message.
Variable s0 : Site.
(* no longer useful 'cos copy is out of band and could be last *)

Lemma in_q_before_append :
forall q1 q2 : queue Message,
In_queue_before Message dec is_inc_dec (append Message q1 q2) ->
In_queue_before Message dec is_inc_dec
(append Message q1 (input Message copy q2)).