Definition val_inject_opt (j: meminj) (v1 v2: option val) :=
  match v1, v2 with Some v1', Some v2' => val_inject j v1' v2'
  | None, None => True
  | _, _ => False
  end.

Lemma fwd_maxpermorder: forall m1 m2 (FWD: mem_forward m1 m2) (b:block) (V:Mem.valid_block m1 b) ofs, Mem.perm_order'' (PMap.get b (Mem.mem_access m1) ofs Max) (PMap.get b (Mem.mem_access m2) ofs Max).