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

Lemma Fn_inv_is_l_inverse :
forall (F : group) (n : Nat),
inverse_l (Fn_plus F n) (Fn_zero F n) (Fn_inv F n).