intros A B C H' H'0 H'1 a b c H'2 H'3 H'4; red in |- *; simpl in |- *.
intros H'5 H'6; exists c; split.
apply Lub_is_in_Carrier with (X := C); auto with sets.
apply Upper_Bound_Couple_intro; auto with sets.
apply Lub_is_in_Carrier with (X := C); auto with sets.
apply Lub_monotonic with (A := A) (B := C); auto with sets.
apply Lub_monotonic with (A := B) (B := C); auto with sets.
Qed.

Lemma LUaux :
forall A B : Ensemble U,
Included U (Union U A B) (Carrier_of U D) ->
forall a b bsup : U,
Lub U D A a ->
Lub U D B b -> Lub U D (Union U A B) bsup -> Lub U D (Couple U a b) bsup.