proposition: Lemma inv_mult_invol : forall x y : R, [--]x[*] [--]y [=] x[*]y.
proof: Proof. intros x y. astepl ( [--] (x[*] [--]y)). Step_final ( [--][--] (x[*]y)). 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)