Section L13_1.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** Pappus Desargues *)

Lemma per3_preserves_bet2_aux : forall O A B C B' C', Col O A C -> A <> C' ->
Bet A B' C' -> O <> A -> O <> B' -> O <> C'
-> Per O B' B -> Per O C' C
-> Col A B C -> Col O A C' -> Bet A B C.