intros...
assert (S4 D C B A = S4 A D C B)...
rewrite H...
Qed.
Hint Resolve S4_6: Geom.

(* Specifications: *)
Lemma S4_7 : forall A B C D : Point, S4 A B C D = - S4 C B A D.
Proof with try solve [ Geometry | congruence ].