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}.

Lemma per2_os__ncol123 : forall A B C D, Per B A D -> Per A D C -> OS A D B C ->
~ Col A B C.