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 per_proj : forall A B T P, A <> B -> Per T P A -> Per T P B -> Col A B P -> proj T A B P.