Section T10.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
Goal forall A B C D, ~ Coplanar D C B A -> ~ Coplanar A B C D.

Lemma l10_15 : forall A B C P,
Col A B C -> ~ Col A B P ->
exists Q, Perp A B Q C /\ OS A B P Q.