Section MapAxioms.
Variables A B C : Type.
Definition eqmap (m m':Map A) := eqm A (MapGet A m) (MapGet A m').

Lemma MapDomRestrBy_Dom :
forall (m:Map A) (m':Map B),
eqmap (MapDomRestrBy A B m m') (MapDomRestrBy A unit m (MapDom B m')).