Definition permMapLt (pmap1 pmap2 : access_map) : Prop :=
    forall b ofs,
      Mem.perm_order'' (Maps.PMap.get b pmap2 ofs)
                       (Maps.PMap.get b pmap1 ofs).

(* Specifications: *)
Lemma empty_LT: forall pmap, permMapLt empty_map pmap.
Lemma canonical_lt : forall p' m (Hlt: permMapLt p' (getMaxPerm m)), isCanonical p'.