+ 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 ple_free: forall m m' b lo hi (FL: Mem.free m b lo hi = Some m') m1 (PLE:perm_lesseq m m1),
exists m1', Mem.free m1 b lo hi = Some m1' /\ perm_lesseq m' m1'.