(* Gabriel Braun March 2013 *)
Require Export GeoCoq.Tarski_dev.Annexes.vectors.
Section Projections.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.

Lemma ker_col : forall P Q P' A B X Y, Proj P P' A B X Y -> Proj Q P' A B X Y -> Col P Q P'.