intros F n.
red in |- *.
intro.
simpl in |- *.
red in |- *.
intro i.
simpl in |- *.
apply MONOID_unit_r.
Qed.

Lemma Fn_zero_is_l_unit :
forall (F : monoid) (n : Nat),
unit_l (sgroup_law_map (Fn_sgroup F n)) (Fn_zero F n).