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'')).