Definition eqmap (m m':Map A) := eqm A (MapGet A m) (MapGet A m').

Lemma MapMerge_RestrTo_l :
forall m m' m'':Map A,
eqmap (MapMerge A (MapDomRestrTo A A m m') m'')
(MapDomRestrTo A A (MapMerge A m m'') (MapMerge A m' m'')).