Definition join (j k:meminj):meminj := fun b =>
match j b with
Some (b1, delta) => Some (b1,delta)
| None => k b
end.
Definition disjoint (j k:meminj):Prop :=
forall b, j b = None \/ k b = None.

Lemma inject_incr_join: forall j j' k k'
(J: inject_incr j j') (K: inject_incr k k')
(D: disjoint j' k'),
inject_incr (join j k) (join j' k').