+ intros. xomega.
+ induction 1.
- apply Mem.nextblock_storebytes in H;
rewrite H; xomega.
- apply Mem.nextblock_alloc in H.
rewrite H. clear. xomega.
- apply nextblock_freelist in H.
rewrite H; xomega.
- xomega.
Qed.

Lemma free_access_inv m b lo hi m' (FR: Mem.free m b lo hi = Some m') b' ofs k p
(P: (Mem.mem_access m') !! b' ofs k = Some p):  (Mem.mem_access m) !! b' ofs k = Some p.