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 five following lemmas come from Theorem 21.8 *)
Lemma lt_os_per2__lta : forall A B C D,
Per B A D -> Per A D C ->
OS A D B C ->
Lt A B C D ->
LtA B C D A B C.