Section Orientation.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.
Definition proj := fun  T A B P => A <> B /\ (~Col A B T /\ Perp A B T P /\ Col A B P \/ Col A B T /\ P = T).

Lemma proj_col_proj : forall A B C T P, proj T A B P -> A <> C -> Col A B C -> proj T A C P.