eapply mem_forward_preserve; trivial.
Qed.

Lemma freelist_perm_inv: forall l m m' (L : Mem.free_list m l = Some m') b (B: Mem.valid_block m b)
ofs k p (P: Mem.perm m b ofs k p),
Mem.perm m b ofs Max Freeable \/ Mem.perm m' b ofs k p.