Definition F (A : Set) (f : ad -> A -> M) (r : ad * A) 
  (m : M) := let (a, y) := r in op (f a y) m.

Lemma myMapFold_as_fold : forall (A : Set) (f : ad -> A -> M) (m : Map A), R (MapFold _ M neutral op f m) (fold_right (fun (r : ad * A) (m : M) => let (a, y) := r in op (f a y) m) neutral (alist_of_Map _ m)).