(* Lemma unchanged_on_sym P m m' b: Mem.unchanged_on P m m' -> Mem.valid_block m b -> Mem.unchanged_on (fun bb z => P bb z /\ bb=b) m' m. *)

Lemma forward_nextblock: forall m m',
mem_forward m m' ->
(Mem.nextblock m <= Mem.nextblock m')%positive.