(* Gabriel Braun April 2013 *)
Require Export GeoCoq.Tarski_dev.Ch12_parallel.
Section L13_1.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** Pappus Desargues *)

Lemma symmetry_preserves_per : forall A P B A' P', Per B P A -> Midpoint B A A' -> Midpoint B P P'
-> Per B P' A'.