Definition PMap_eq {A} (m m' : PMap.t (Z -> A)) := forall b' ofs', m !! b' ofs' = m' !! b' ofs'.

Lemma setPerm_congr b o e e':
PMap_eq e e' ->
PMap_eq (setPerm (Some Writable) b o e)
(setPerm (Some Writable) b o e').