Lemma MapFold_Merge_disjoint_1 : forall (f:ad -> A -> M) (m1 m2:Map A) (pf:ad -> ad), MapDisjoint A A m1 m2 -> MapFold1 A M neutral op f pf (MapMerge A m1 m2) = op (MapFold1 A M neutral op f pf m1) (MapFold1 A M neutral op f pf m2).