(* Lemma test_on_line_d_13 : forall Y P Q A C D lambda, on_line_d Y P Q lambda ->  Y<>A -> parallel C D Y A -> False -> C**D/Y**A = C**D. *)
(** Test inter_ll in a ratio *)
(** Test cases where Y occurs both in denominator and numerator *)

Lemma test_inter_ll_3b :  forall Y P Q U V,
inter_ll Y P Q U V ->  Q<>Y -> parallel Y P Q Y ->
Y**P/Q**Y = - (S P U V / S Q U V).