proposition: Lemma same_side_sym : forall A B l, same_side A B l -> same_side B A l.
proof: Proof. intros. apply one_side_same_side. apply same_side_one_side in H. apply one_side_symmetry. assumption. Qed.
imports: Morphisms GeoCoq.Axioms.hilbert_axioms GeoCoq.Axioms.parallel_postulates GeoCoq.Meta_theory.Parallel_postulates.tarski_playfair GeoCoq.Meta_theory.Parallel_postulates.SPP_ID GeoCoq.Meta_theory.Dimension_axioms.upper_dim_3 GeoCoq.Meta_theory.Parallel_postulates.parallel_postulates GeoCoq.Utils.triples