Definition func_sgroup (A : Setoid) (B : sgroup) : SGROUP :=
  Build_sgroup (Build_sgroup_on (func_plus_associative (A:=A) (B:=B))).

(* Specifications: *)
Lemma func_plus_commutative : forall (A : Setoid) (B : abelian_sgroup), commutative (func_plus A B).