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

Lemma two_sides_in_angle : forall A B C P P',
B <> P' ->
TS B P A C ->
Bet P B P' ->
InAngle P A B C \/ InAngle P' A B C.