Require Export GeoCoq.Tarski_dev.Ch12_parallel.
Require Export GeoCoq.Tarski_dev.Annexes.suma.
(** This development is inspired by The Foundations of Geometry and the Non-Euclidean Plane, by George E Martin, chapters 21 and 22 *)
Section Saccheri.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

(** The two following lemmas come from Theorem 21.10 *)
Lemma sac__cong : forall A B C D, Saccheri A B C D -> Cong A C B D.