Proof with Geometry.
intros.
apply l1_25...
Qed.

(* Specifications: *)
Theorem thales_2 :
forall S A B A' B' : Point,
~ Col S A A' ->
Col S A B ->
Col S A' B' ->
parallel A A' B B' ->
S ** B / S**A  = S ** B' / S**A'.