Definition copy_trans (c : Config) (s1 s2 : Site) :=
  mkconfig (S (time c)) (dt c) (Inc_send_table (st c) s1) 
    (rt c) (Post_message copy (bm c) 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.