unfold Same_dir in H.
induction H.
tauto.
ex_and H D.
apply null_vector in H0.
subst D.
unfold Out in H.
tauto.
Qed.

Lemma plg_out_plg :
forall A B C D B' C',
Parallelogram A B C D ->
Out A B B' ->
Out D C C' ->
Cong A B' D C' ->
Parallelogram A B' C' D.