Require Export GeoCoq.Elements.OriginalProofs.lemma_angletrichotomy.
Require Export GeoCoq.Elements.OriginalProofs.proposition_18.
Require Export GeoCoq.Elements.OriginalProofs.lemma_trichotomy1.
Section Euclid.
Context `{Ax:euclidean_neutral_ruler_compass}.

Lemma proposition_19 :
forall A B C,
Triangle A B C -> LtA B C A A B C ->
Lt A B A C.