Section MapDisjointExtra.
Variables A B : Type.
Variable C : Type.
Variable D : Type.

Lemma MapSubset_Disjoint :
forall (m:Map A) (m':Map B) (m'':Map C) (m''':Map D),
MapSubset _ _ m m' ->
MapSubset _ _ m'' m''' ->
MapDisjoint _ _ m' m''' -> MapDisjoint _ _ m m''.