proposition: Lemma L1ball_sym : forall e x y, (L1Ball e x y) -> (L1Ball e y x).
proof: Proof. intros e x y. unfold L1Ball, L1Distance. unfold L1Norm. setoid_replace (x-y) with (-(y-x)); [| ring]. rewrite -> StepQabsOpp. auto. Qed.
imports: CoRN.algebra.RSetoid CoRN.metric2.Metric CoRN.metric2.UniformContinuity CoRN.model.totalorder.QposMinMax CoRN.model.structures.StepQsec CoRN.metric2.UniformContinuity CoRN.metric2.Prelength CoRN.model.structures.OpenUnit Coq.QArith.QArith CoRN.model.totalorder.QMinMax Coq.QArith.Qabs CoRN.model.ordfields.Qordfield CoRN.model.metric2.Qmetric CoRN.algebra.COrdFields2 CoRN.tactics.CornTac