proposition: Lemma concy_bd : forall (A : Tpoint) (X : cartesianPower Tpoint 2), app_2_n concy A A X.
proof: Proof. unfold app_2_n, concy; simpl; intros; apply concyclic_gen_1123. Qed.
imports: GeoCoq.Tactics.Coinc.tactics_axioms GeoCoq.Tarski_dev.Annexes.inscribed_angle