Definition Parallelogramm := fun A B C D : Point =>
	Clockwise A B C /\
	Clockwise A C D /\
	Distance A B = Distance C D /\
	Distance A D = Distance B C.

(* Specifications: *)
Lemma ParallelogrammCongruentTrianglesAC : forall A B C D : Point, Parallelogramm A B C D -> CongruentStrictTriangles A B C C D A.
Lemma ParallelogrammCongruentTrianglesBD : forall A B C D : Point, Parallelogramm A B C D -> CongruentTriangles D A B B C D.