Hint Resolve perp_per_1 perp_per_2 perp_col perp_perp_in perp_in_perp : perp.
Section T8_5.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma col_per2__per : forall A B C P X, A <> B -> Col A B C -> Per A X P -> Per B X P -> Per C X P.