Module Export FM := Dec.F.
Definition set_of_points := t.
Definition Point := DecPoints.t.
Definition couple(x y :Point) : set_of_points :=
add x (add y empty).
Definition triple(x y t :Point): set_of_points :=
add x (add y (add t empty)).

Lemma test : forall P A B C A' B' C',
Equal
(union (singleton P) (union (triple A B C) (triple A' B' C')))
(union (triple P B B') (union (couple P A) (triple C A' C'))).