(* We do not need that Col A B C. *)

(* Specifications: *)
Lemma chasles_ratios : forall A B C P Q,
P <> Q -> ratio A B P Q + ratio B C P Q =F= ratio A C P Q.
Lemma ratio_zero : forall A B C D, C<>D -> AM_Par A B C D ->  (ratio A B C D =F= 0 -> A = B).
Lemma axiom_A2b : forall A B P P' r,
A<>B -> Col A B P ->
ratio A P A B =F= r ->
Col A B P' ->
ratio A P' A B =F= r ->
P = P'.