Section Inscribed_angle.
Context `{TE:Tarski_euclidean}.
(** The sum of the angles of a triangle is the flat angle. *)
(** If A, B and C are points on a circle where the line AB is a diameter of the circle, then the angle ACB is a right angle. *)
(** In a right triangle, the midpoint of the hypotenuse is the circumcenter. *)

Lemma thales_converse_theorem_1 : forall A B C O, A <> C -> B <> C ->
Per A C B -> Cong O A O B -> Cong O A O C -> Coplanar A B C O -> Midpoint O A B.