Variable comm : forall a b:M, op a b = op b a.

Lemma MapFold_Put_behind_disjoint_2 :
forall (f:ad -> A -> M) (m:Map A) (a:ad) (y:A) (pf:ad -> ad),
MapGet A m a = None ->
MapFold1 A M neutral op f pf (MapPut_behind A m a y) =
op (f (pf a) y) (MapFold1 A M neutral op f pf m).