Definition inj_offset_aligned (delta: Z) (size: Z) : Prop :=
forall chunk, size_chunk chunk <= size -> (align_chunk chunk | delta).

Axiom drop_outside_inject:
forall f m1 m2 b lo hi p m2',
inject 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) ->
inject f m1 m2'.