(* Gabriel Braun November 2012 *)
Require Export GeoCoq.Tarski_dev.Ch12_parallel.
Section Quadrilateral.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma plgf_sym :
forall A B C D,
Parallelogram_flat A B C D ->
Parallelogram_flat C D A B.