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_le_dt_time : forall s0 : Site, dt c0 s0 <= time c0 -> dt (copy_trans c0 s1 s2) s0 <= time (copy_trans c0 s1 s2).