Theorem th6_259 : forall A B C D E F G H R L : Point, on_parallel_d E A B D 1 -> on_parallel_d G A C F 1 -> inter_ll H D E F G -> inter_ll R B C H A -> on_parallel_d L B H A 1 -> S F A B <> 0 -> S A C F + S B A D = S C B L.