proposition: Lemma line_extension_symmetry : forall {Tm : Tarski_neutral_dimensionless} (f : @Tpoint Tn -> @Tpoint Tm) P Q, line_extension f P Q -> line_extension f Q P.
proof: Proof. intros Tm f P Q [HPQ [fInj [fBet fCong]]]. repeat split; auto; intro; intros; [apply fInj|apply fBet|apply fCong]; Col. Qed.
imports: GeoCoq.Axioms.continuity_axioms GeoCoq.Meta_theory.Dimension_axioms.upper_dim_2 GeoCoq.Meta_theory.Dimension_axioms.upper_dim_3 GeoCoq.Meta_theory.Continuity.grad