proposition: Lemma zring_minus : 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)