proposition: Lemma retract_is_int: Integers Z2 (U:=retract_is_int_to_ring).
proof: Proof. split;try apply _. - unfold integers_to_ring, retract_is_int_to_ring. apply _. - intros;apply same_morphism;apply _. Qed.
imports: HoTT.Basics.Decidable HoTT.Classes.theory.nat_distance HoTT.Classes.implementations.peano_naturals HoTT.Classes.interfaces.naturals HoTT.Classes.interfaces.orders HoTT.Classes.implementations.natpair_integers HoTT.Classes.theory.rings HoTT.Classes.isomorphisms.rings HoTT.Classes.interfaces.integers