proposition: Lemma zring_inv : forall i, zring (- i) [=] [--] (zring i).
proof: Proof. intro i. astepl (zring_old (- i)). Step_final ( [--] (zring_old i)). 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)