proposition: Lemma retract_is_nat : Naturals SR (U:=retract_is_nat_to_sr).
proof: Proof. split;try apply _. - unfold naturals_to_semiring, retract_is_nat_to_sr. apply _. - intros;apply same_morphism;apply _. 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