Section PARALLELOGRAMM.
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.

Lemma ParallelogrammCongruentTrianglesBD : forall A B C D : Point,
Parallelogramm A B C D ->
CongruentTriangles D A B B C D.