End T1_3.
Hint Resolve cong_3_sym : cong.
Hint Resolve cong_3_swap cong_3_swap_2 cong3_transitivity : cong3.
Hint Unfold Cong_3 : cong3.
Section T1_4.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma l2_11 : forall A B C A' B' C',
Bet A B C -> Bet A' B' C' -> Cong A B A' B' -> Cong B C B' C' -> Cong A C A' C'.