(* 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 alloc_readonly:
forall m lo hi m' b
(A: Mem.alloc m lo hi = (m',b)),
forall b, Mem.valid_block m b -> readonly m b m'.