End T11_1.
Section T11_2.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma inangle_one_side2 : forall A B C P Q , ~ Col A B C -> ~ Col A B P -> ~ Col A B Q ->
~ Col C B P -> ~ Col C B Q ->
InAngle P A B C -> InAngle Q A B C ->
OS A B P Q /\ OS C B P Q.