(*memories that do not contain "dangling pointers"*)
Definition mem_wd m := Mem.inject_neutral (Mem.nextblock m) m.

Lemma free_neutral: forall (thr : block) (m : mem) (lo hi : Z) (b : block) (m' : Mem.mem')
(FREE: Mem.free m b lo hi = Some m'),
Mem.inject_neutral thr m -> Mem.inject_neutral thr m'.