Section INVARIANT5.
(* In this file, we establish the following inequality Int + Sum copy + Sum dec - Sum inc_dec >= 0  *)
(* The message queue between a site and the owner has a particular structure.  Messages dec and inc_dec are alternated. *)

Lemma legal_alternate :
forall (s : Site) (c : Config),
legal c ->
alternate (bm c s owner) /\ (rt c s = false -> D_queue (bm c s owner)).