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

Lemma parallelogram_strict_not_col_3 : forall A B C D,
Parallelogram_strict A B C D ->
~ Col C D A.