proposition: Lemma dist_2b : forall x y z : R, (x[-]y) [*]z [=] x[*]z[-]y[*]z.
proof: Proof. intros x y z. astepl (z[*] (x[-]y)). Step_final (z[*]x[-]z[*]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)