Require Export GeoCoq.Elements.OriginalProofs.lemma_angleordertransitive.
Require Export GeoCoq.Elements.OriginalProofs.lemma_sameside2.
Require Export GeoCoq.Elements.OriginalProofs.proposition_07.
Section Euclid.
Context `{Ax:euclidean_neutral_ruler_compass}.

Lemma lemma_angletrichotomy :
forall A B C D E F,
LtA A B C D E F ->
~ LtA D E F A B C.