(* 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 loadbytes_unchanged_on (P : block -> Z -> Prop) m m' b ofs n:
Mem.unchanged_on P m m' -> Mem.valid_block m b ->
(forall i : Z, ofs <= i < ofs + n -> P b i) ->
Mem.loadbytes m b ofs n = Mem.loadbytes m' b ofs n.