(** We show here that from the axioms of neutral geometry we can deduce the existence of a parallel line. This is important because it shows that axioms of neutral geometry are inconsistent with those of elliptic geometry as elliptic geometry assumes that no parallel lines exist. *)
(** This corresponds to l12_10 in Tarski's book. *)

Lemma par_col4__par : forall A B C D E F G H, E <> F -> G <> H -> Par A B C D ->
Col A B E -> Col A B F -> Col C D G -> Col C D H -> Par E F G H.