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

Lemma is_image_perp_in : forall A A' X Y, A <> A' -> X <> Y -> Reflect A A' X Y ->
exists P, Perp_at P A A' X Y.