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

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