Definition permMapCoherence (pmap1 pmap2 : access_map) :=
forall b ofs, perm_coh (pmap1 !! b ofs) (pmap2 !! b ofs).

Lemma permCoh_empty: forall r,
(forall b ofs, Mem.perm_order'' (Some Writable) (r !! b ofs)) ->
permMapCoherence empty_map r.