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 bet_cong__ghalfa : forall A B C B', A <> B -> B <> C -> A <> B' ->
Bet B A B' -> Cong A B A C -> gHalfA A B C C A B'.