proposition: Lemma zring_plus_nat : forall n : nat, zring n [=] nring n.
proof: Proof. intro n; Step_final (zring_old n). Qed.
imports: CoRN.tactics.CornTac CoRN.algebra.CSums CoRN.algebra.CAbMonoids Coq.Sorting.Permutation CoRN.util.SetoidPermutation Coq.Setoids.Setoid Coq.Classes.Morphisms Coq(Lia)