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 D_shuffle_copy1 :
forall q1 q2 : queue Message,
D_queue (input Message copy (append Message q1 q2)) ->
D_queue (append Message q1 (input Message copy q2)).