Definition MapDisjoint (m:Map A) (m':Map B) :=
    forall a:ad, in_dom A a m = true -> in_dom B a m' = true -> False.Definition MapDisjoint_1 (m:Map A) (m':Map B) :=
    match MapSweep A (fun (a:ad) (_:A) => in_dom B a m') m with
    | None => true
    | _ => false
    end.Definition MapDisjoint_2 (m:Map A) (m':Map B) :=
    eqmap A (MapDomRestrTo A B m m') (M0 A).

Lemma MapDisjoint_M2 : forall (m0 m1:Map A) (m2 m3:Map B), MapDisjoint A B m0 m2 -> MapDisjoint A B m1 m3 -> MapDisjoint A B (M2 A m0 m1) (M2 B m2 m3).