Require Export GeoCoq.Elements.OriginalProofs.lemma_extension.
Require Export GeoCoq.Elements.OriginalProofs.lemma_collinearorder.
Section Euclid.
Context `{Ax:euclidean_neutral_ruler_compass}.

Lemma proposition_11 :
forall A B C,
BetS A C B ->
exists X, Per A C X.