Section Projections.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.

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