(* The proof is long and very boring, but it is a simple case analysis.  Could it be possible to simplify it? *)

Lemma inc_dec_owner2 :
forall (c : Config) (s1 s2 : Site),
legal c ->
s1 <> owner ->
s2 <> owner ->
forall s0 : Site, ~ In_queue Message (inc_dec s0) (bm c s1 s2).