intros X H' H'0; elim H'0; intros maj E; try exact E; clear H'0.
red in |- *; simpl in |- *.
intros H'0 x y H'1; red in |- *; simpl in |- *.
intros H'2 H'3; exists maj; split.
elim E; auto with sets.
elim E; auto with sets.
Qed.

Lemma Consistent_triple_intro :
forall x y z : U,
Compatible U D x y ->
Compatible U D y z -> Compatible U D x z -> Consistent U D (Triple U x y z).