proposition: Lemma Qabs_Qminus x y: Qabs (x - y) == Qabs (y - x).
proof: Proof. unfold Qminus. intros. rewrite <- (Qopp_opp x) at 1. rewrite <- Qopp_plus. rewrite Qplus_comm. apply Qabs_opp. Qed.
imports: Coq.QArith.QArith Coq.ZArith.ZArith Coq.NArith.NArith Coq.QArith.Qpower Coq.QArith.Qround Coq.QArith.Qround Coq.QArith.Qabs CoRN.stdlib_omissions.List