Lemma l6_44 : forall A B C G P Q I J, is_midpoint J A C -> is_midpoint I B C -> inter_ll G J B I A -> on_inter_line_parallel P G A B B C -> on_inter_line_parallel Q G A C B C -> G<>P -> G<>Q -> (2+2)*S4 P Q C B = (2+2+1)*S A Q P.