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

Lemma conga_preserves_in_angle : forall A B C I A' B' C' I',
CongA A B C A' B' C' -> CongA A B I A' B' I' ->
InAngle I A B C -> OS A' B' I' C' ->
InAngle I' A' B' C'.