+ 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_freelist: forall l m m' (FL: Mem.free_list m l = Some m') m1 (PLE:perm_lesseq m m1),
exists m1', Mem.free_list m1 l = Some m1' /\ perm_lesseq m' m1'.