proposition: Lemma zring_mult : forall i j, zring (i * j) [=] zring i[*]zring j.
proof: Proof. intros i j. astepl (zring_old (i * j)). Step_final (zring_old i[*]zring_old j). 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)