proposition: Lemma CRing_is_CRing : is_CRing R [1] cr_mult.
proof: Proof. elim R; auto. 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)