Section MapSubsetExtra.
Variables A B : Type.
Variables C D : Type.

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