End my_MapFold.
(* Next we show the assumptions in the previous section are satisfied if M is a set of maps, neutral is the empty map, op is MapMerge and R is eqmap *)

(* M0 is the left identity *)
Lemma MapMerge_neutral_left :
forall (A : Set) (m : Map A), eqmap _ (MapMerge _ (M0 A) m) m.