(** Preservation of [drop_perm] operations. *)

Lemma drop_outside_inj: forall f m1 m2 b lo hi p m2',
mem_inj f m1 m2 ->
drop_perm m2 b lo hi p = Some m2' ->
(forall b' delta ofs' k p,
f b' = Some(b, delta) ->
perm m1 b' ofs' k p ->
lo <= ofs' + delta < hi -> False) ->
mem_inj f m1 m2'.