Proof with Geometry.
intros.
apply  weak_2_parallelogram_weak_3_parallelogram.
apply weak_parallelogram_weak_2_parallelogram.
assumption.
Qed.

(* Specifications: *)
Lemma parallelogram_weak_3_parallelogram :
forall A B C D, parallelogram A B C D ->
weak_3_parallelogram A B  C D.