Section T8_4.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma perp_col4 : forall A B C D P Q R S, P <> Q -> R <> S ->
Col A B P -> Col A B Q -> Col C D R -> Col C D S -> Perp A B C D -> Perp P Q R S.