Definition Concat_map2 := Build_Map2 Concat_congl Concat_congr.

(* Specifications: *)
Lemma Mass_FreeMonoid : Monoid_ass Concat_map2.
Lemma Midl_FreeMonoid : Monoid_idl Concat_map2 Empty.
Lemma Midr_FreeMonoid : Monoid_idr Concat_map2 Empty.