Require Export GeoCoq.Elements.OriginalProofs.lemma_parallelflip.
Require Export GeoCoq.Elements.OriginalProofs.lemma_parallelsymmetric.
Section Euclid.
Context `{Ax1:euclidean_neutral}.

Lemma lemma_PGflip :
forall A B C D,
PG A B C D ->
PG B A D C.