proposition: Lemma negate_to_ring x y : -f x = f y -> f x = f y.
proof: Proof. intros E. destruct (to_ring_zero_sum x y E) as [E2 E3]. rewrite E2, E3. reflexivity. Qed.
imports: HoTT.Basics.Decidable HoTT.Classes.interfaces.orders HoTT.Classes.implementations.peano_naturals HoTT.Classes.theory.rings HoTT.Classes.isomorphisms.rings HoTT.Classes.interfaces.naturals