intros H' C bsup1 bsup2 H'0 H'1.
apply (Rel_of_antisymmetric U D); (elim H'1; elim H'0; auto with sets).
Qed.

Theorem Upper_Bound_Couple_intro :
forall x y z : U,
In U (Carrier_of U D) x ->
In U (Carrier_of U D) y ->
In U (Carrier_of U D) z ->
Rel_of U D x z -> Rel_of U D y z -> Upper_Bound U D (Couple U x y) z.