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 ParallelogrammCongruentTrianglesAC : forall A B C D : Point,
Parallelogramm A B C D ->
CongruentStrictTriangles A B C C D A.