Require Export GeoCoq.Tarski_dev.Annexes.circles.
Require Export GeoCoq.Tarski_dev.Annexes.half_angles.
Require Export GeoCoq.Tarski_dev.Ch12_parallel_inter_dec.
Section Inscribed_angle.
Context `{TE:Tarski_euclidean}.
(** The sum of the angles of a triangle is the flat angle. *)

Lemma right_saccheris : forall A B C D, Saccheri A B C D -> Per A B C.