proposition: Lemma addfraction_law_r : forall x y y' : fraction_set, Equal y y' -> Equal (addfraction_fun x y) (addfraction_fun x y').
proof: Proof. intros x y y' H'; try assumption. apply Trans with (addfraction_fun y x). apply addfraction_fun_com. apply Trans with (addfraction_fun y' x). apply addfraction_law_l; auto with algebra. apply addfraction_fun_com. Qed.
imports: Integral_domain_facts Cfield_cat Abelian_group_facts Ring_util