Atlantic City Electric Co. (P) alleged damages resulting from General Electric's (D) actions. D presented interrogatories to discover if P had passed through the damages to its customers, thus precluding a recovery or invoking setoffs. P objected to the interrogatories, and the district court sustained that objection and certified the ruling for immediate appeal under 28 U.S.C. section 1292(b); it involved a controlling question of law with substantial latitude for differing opinions. D appealed.