Section COPY_EFFECT.
(* invariants *)
Variable c0 : Config.
Variable s1 s2 : Site.
Hypothesis diff_s1_s2 : s1 <> s2.

Lemma copy_trans_diff_site :
forall s3 s4 : Site,
(In_queue Message copy (bm c0 s3 s4) -> s3 <> s4) ->
In_queue Message copy (bm (copy_trans c0 s1 s2) s3 s4) -> s3 <> s4.