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 *)

(* MapMerge preserves the eqmap relation *)
Lemma MapMerge_eq :
forall (A : Set) (a a1 b b1 : Map A),
eqmap _ a a1 -> eqmap _ b b1 -> eqmap _ (MapMerge _ a b) (MapMerge _ a1 b1).