intros.
red in |- *.
intro.
simpl in |- *.
red in |- *.
intro i.
simpl in |- *.
auto with algebra.
Qed.

Lemma func_inv_is_l_inverse :
forall (A : Setoid) (B : group),
inverse_l (func_plus A B) (func_zerofun A B) (func_inv A B).