Kroger's (P) husband was electrocuted when the boom of a steel crane came too close to a high-tension electric power line of the Omaha Public Power District (D). P was a citizen of Iowa. The crane was operated by Owen (D1). P brought a wrongful death action against D in federal court in Nebraska. D then filed a third-party complaint against D1, alleging its negligence had caused the electrocution. P then amended her complaint to also name D1. D's motion for summary judgment was granted, and D1 was the only defendant left in the case. During trial, it was discovered that D1, a Nebraska corporation, had its principal place of business in Iowa and was a citizen of the same state as P. D1 moved to dismiss for lack of diversity jurisdiction. The district court denied D1's motion to dismiss the complaint for lack of jurisdiction. The jury gave the verdict to P, and the court of appeals affirmed: Under Mine Workers v. Gibbs, 383 U. S. 715, the District Court had jurisdictional power, in its discretion, to adjudicate the claim, which arose from the 'core of operative facts' giving rise to both claims.