In November, 1953, plaintiff’s intestate, a brakeman employed by the Long Island Railroad Company, was killed when he was knocked from the side of a moving freight car by a gate post located on the land of McKeon Lumber Company. Under the Federal Employers’ Liability Act, 45 U.S.C.A. § 51 et seq., the plaintiff-administratrix, a citizen of New York, brought an action against the defendant as trustee of the Railroad. The defendant filed a third-party complaint against the Lumber Company, claiming full indemnity for any loss for which it might be held liable to the plaintiff. Both the Railroad and the Lumber Company were citizens of New York. With the litigation in this posture, the plaintiff’s action was settled for $30,000; thereafter the third-party action was tried to the court, upon an agreed stipulation of the facts. Judge Abruzzo decided that both the Railroad and the Lumber Company were at fault. The situation, he held, was governed by the terms of a written agreement between the parties which provided that “if any * * * liability * * * shall arise from the joint or concurring negligence of both parties it * * * shall be borne equally.” His judgment therefore provided that each should contribute $15,000 to this settlement. From this judgment the Railroad appeals claiming to be entitled to complete indemnity.
The district court’s jurisdiction over the third-party complaint was not questioned below but at our request the point was briefed by the parties and is before us now. The questions for decision are whether the district court had jurisdiction to entertain the third-party complaint, independent grounds of federal jurisdiction being absent;1 and whether federal jurisdiction over the third-party claim, if it once attached, survived the settlement of the main action upon which federal jurisdiction depended. We think that both questions must be answered in the affirmative.
The contemporary sanction for third-party procedure in the federal courts is Rule 14 of the Federal Rules of Civil Procedure, 28 U.S.C.A. which provides that a defendant with the permission of the court, on a claim arising out of the transaction or occurrence that is the subject matter of the plaintiff’s claim against the third-party plaintiff, may implead a person not theretofore a party to the action who “is or may be liable to him for all or part of the plaintiff’s claim against him.”2 The general purpose of the rule was “to avoid two actions which should be tried together to save the time and cost of a reduplication of evidence, to *807obtain consistent results from identical or similar evidence, and to do away with the serious handicap to a defendant of a time difference between a judgment against him and a judgment in his favor against the third-party defendant.” 3 Moore’s Federal Practice, jf 14.04.
To understand the basic theory of Rule 14 it is necessary to remember that in the Federal Rules of Civil Procedure the word “claim” has a somewhat broader connotation than that which pri- or to the Rules pertained to a “cause of action.” “It is used to denote the aggregate of operative facts which give rise to a right enforceable in the courts.” Original Ballet Russe v. Ballet Theatre, 2 Cir., 133 F.2d 187, 189. As this court noted in Clark v. Taylor, 2 Cir., 163 F.2d 940, 942: “The theory adopted in the new rules * * * has been that the ‘transaction’ or ‘occurrence’ is the subject matter of a claim, rather than the legal rights arising therefrom; additions to or subtractions from the central core of fact do not change this substantial identity * * *.” American Fidelity & Casualty Co. v. Owensboro Milling Co., 6 Cir., 222 F.2d 109; 2 Moore’s Federal Practice, page 359 et seq. The same aggregate or core of facts may give rise not only to rights in the plaintiff against the defendant but also to rights in the defendant against third parties. Under Rule 14, as amended, in the discretion of the court a defendant in the very action which determines the plaintiff’s right against him may have a determination of any right of his against another which arises out of the same transaction or set of facts which gave rise to the plaintiff’s claim. It is the theory of the Rule that the defendant’s right against the third party is merely the outgrowth of the same aggregate or core of facts which is determinative of the plaintiff’s claim. In this view, the court which has jurisdiction over the aggregate of facts which constitutes the plaintiff’s claim needs no additional ground of jurisdiction to determine the third-party claim which comprises the same core of facts. It is, we think, in this sense that the court is said to have ancillary jurisdiction over the third-party claim.
The great weight of authority amongst the federal district courts is to the effect that when federal jurisdiction over the subject-matter of the main action once attaches the court has ancillary jurisdiction to decide a third-party dispute growing out of the same core of facts and hence within the scope of the Rule even though the dispute, separately considered, is lacking in the attributes of federal jurisdiction. This appears from the cases listed in 3 Moore’s Federal Practice, ¶ 14.26 n. 6 and 1958 Supplement, page 496. See also Foster v. Brown, Chesnut, Judge, D.C.D.Md., 22 F.R.D. 471. In a number of appellate court opinions there is discussion which clearly supports that conclusion. Lesnik v. Public Industrial Corp., 2 Cir., 144 F. 2d 968; Walmac Co. v. Isaacs, 1 Cir., 220 F.2d 108; United States v. Acord, 10 Cir., 209 F.2d 709, certiorari denied 347 U.S. 975, 74 S.Ct. 766, 98 L.Ed. 1115; Sheppard v. Atlantic States Gas Co., 3 Cir., 167 F.2d 841; Williams v. Keyes, 5 Cir., 125 F.2d 208, certiorari denied 316 U.S. 699, 62 S.Ct. 1297, 86 L.Ed. 1768. Cf. American Fidelity & Casualty Co. v. Owensboro Milling Co., supra. In Bernstein v. N. V. Nederlandsche-Amerikaansche, 2 Cir., 173 F.2d 71, this court recognized the presence of ancillary jurisdiction over a third-party claim thus importing that no independent ground of jurisdiction was required, although, as it happened, an independent ground, diversity, was there present.
Our conclusion as to the ancillary character of a third-party claim under Rule 14 is fortified by cases in the cognate field of compulsory counterclaims under Rule 13. This court is committed to the majority rule that such a counterclaim — even one which impleads a new party 3 — may rest on ancillary jurisdiction without need for an independent *808ground of federal jurisdiction. United Artists Corp. v. Masterpiece Productions, Inc., 2 Cir., 221 F.2d 213; Lesnik v. Public Industrial Corp., 2 Cir., 144 F.2d 968, 975. See Moore v. New York Cotton Exchange, 270 U.S. 593, 46 S.Ct. 367, 70 L.Ed. 750; 3 Moore’s Federal Practice, 13.15.
A rüle of procedure, of course, however convenient and salutary it may be, is without efficacy to extend the jurisdiction of a court. See Hurn v. Oursler, 289 U.S. 238, 53 S.Ct. 586, 77 L.Ed. 1148; Fed.Rules Civ.Proc., Rule 82. But Rule 14 does not extend jurisdiction. It merely sanctions an impleader procedure which rests upon the broad conception of a claim as comprising a set of facts giving rise to rights flowing both to and from a defendant. For solution of the incidental jurisdictional problems which often attend utilization of the procedure, the concept of ancillary jurisdiction, which long antedated the Federal Rules, may often be drawn upon. See, e. g., Dewey v. West Fairmont Gas Coal Co., supra; Moore v. New York Cotton Exchange, supra; Empire Lighting Fixture Co. v. Practical Lighting Fixture Co., 2 Cir., 20 F.2d 295; Lesnik v. Public Industrial Corp., supra; 3 Moore’s Federal Practice, ¶ 14.02; The Ancillary Concept and the Federal Rules, 64 Harv.L.Rev. 968. In this case, we hold, the jurisdiction which the court below had acquired over the plaintiff’s claim was broad enough to comprehend jurisdiction of the ancillary third-party claim and that the ancillary jurisdiction attached when the impleader was accomplished.
We also hold that the ancillary jurisdiction over the third-party complaint was not lost when the main cause of action was settled. Generally, in a diversity action, if jurisdictional prerequisites are satisfied when the suit is begun, subsequent events will not work an ouster of jurisdiction. Mullen v. Torrance, 9 Wheat. 536, 6 L.Ed. 154; St. Paul Mercury Indemnity Co. v. Red Cab Co., 303 U.S. 283, 58 S.Ct. 586, 82 L.Ed. 845; Hardenbergh v. Ray, 151 U. S. 112, 14 S.Ct. 305, 38 L.Ed. 93. This result is not attributable to any specific statute or to any language in the statutes which confer jurisdiction. It stems rather from the general notion that the sufficiency of jurisdiction should be determined once and for all at the threshold and if found to be present then should continue until final disposition of the action. Moreover, in cases involving the impact of jurisdictional problems on the joinder of claims under Rule 18 it has been held that jurisdiction of the ancillary claim survives the final disposition of the main claim. American Fidelity & Casualty Co. v. Owensboro Milling Co., supra; Lindquist v. Dilkes, 3 Cir., 127 F.2d 21. In principle, the same rule would seem to be applicable to third-party claims which under Rule 14 must rest on the same transaction or set of facts as the main claim and thus fall within the “first category” described in Hurn v. Oursler, supra, 289 U.S. at page 246, 53 S.Ct. at page 590.
Considerations of policy, as well as the foregoing analogies, accord with our conclusion. If the main claim and the third-party claim are tried together and a decision or a settlement in favor of the plaintiff is announced on the main claim in advance of decision of the third-party claim, to hold that the determination of the main claim ousted the court of jurisdiction over the ancillary claim would in many cases entail a serious waste of effort by both the judge and the litigants. The natural tendency would be to discourage settlements. And the same considerations, though perhaps to a lesser degree, would tend to discourage adjudications on motions and settlements in advance of trial. Confusion would result from such doctrine not only as to the timing but also as to the nature of the event causing loss of the ancillary jurisdiction. If the jurisdictional loss were held not to flow from a settlement of the main claim after trial, can it consistently be held that a settlement thereof at some pre-trial stage will operate to terminate jurisdiction over the third-party claim? Is an out-of-court agreement of settlement an operative jurisdic*809tional factor, or must the agreement be translated into a judicial order to dismiss the claim as moot or to enforce the settlement? Not infrequently, if ancillary jurisdiction were thus subject to defeasance, the third-party claim might be time-barred although, to be sure, that seems not to be an immediate hazard in this case. In short, a rule that ancillary jurisdiction of a third-party claim terminates on a determination of the main claim will seriously impair the utility of the Rule, breed confusion and generate many sterile jurisdictional disputes.
We find no authority in conflict with our holding. It is true that there are a number of cases holding that a court, just as it has discretion under Rule 14 to implead a third-party, may in its discretion dismiss the third-party complaint. In some cases the discretion to dismiss has been exercised. Duke v. Reconstruction Finance Corp., 4 Cir., 209 F.2d 204; 4 State of Maryland to Use and Benefit of Wood v. Robinson, D.C.D.Md., 74 F.Supp. 279, 281-282; E. K. Carey Drilling Co. v. Murphy, D.C.D.Colo., 113 F.Supp. 226. In other cases, the court in the exercise of its discretion has retained jurisdiction. Oakes v. Graham Towing Co., D.C.E.D.Pa., 135 F.Supp. 485.5 But this appeal involves no question as to such discretionary power in a trial court. No motion to dismiss was made below and the judge, instead of entering a discretionary dismissal, proceeded to try the third-party claim. We think the original ancillary jurisdiction survived.
The merits of the appeal present little difficulty. The plaintiff’s intestate, a freight brakeman, was killed by being knocked off the side of a freight car which the Railroad was moving into a sidetrack which served the Lumber Company yard. The sidetrack was the subject matter of a contract between the Railroad and Lumber Company which provided that the Lumber Company should “not erect or allow to be erected” any fixture nearer than eight feet from the center of the track. Notwithstanding, the Lumber Company had erected a gatepost which was only about seven feet from the center of the track and it was this post by which, several years subsequent to its erection, the intestate, on the moving freight car, had been knocked to his death. Under the sidetrack agreement the Railroad had the right to relocate the post at the Lumber Company’s expense, but although it had inspected the sidetrack monthly for years and had used it daily for the transportation of freight, it had acquiesced in the location of the gatepost without complaint to the Lumber Company. The agreement, in a standard form, contained provisions for indemnity and contribution set forth in the margin.6
The judge below found that the accident had been caused by the “concurring negligence of both parties” to the sidetrack agreement and hence was subject *810to a provision therein that a loss so caused “shall be borne equally by the Industry [Lumber Company] and the Railroad Company.” This finding reasonably followed from the underlying facts as stipulated. And as the judge observed in the opinion below, his conclusion was in accord with the recent opinion of this court in Wanser v. Long Island Railroad Co., 2 Cir., 238 F.2d 467, in which we construed and applied the identical provisions for indemnity and contribution in another sidetrack agreement of this same appellant. The only differences of fact in the case before us are not such as to lead to a different result. The Railroad was negligent in moving the car in which the intestate was riding past the post and negligent in not earlier having taken steps to remove the post or cause its relocation. And the Lumber Company was negligent in erecting the post too close for safety and thereafter in maintaining it for years in that proscribed location. Surely, the conclusion of concurring negligence was proper.
As also indicated in the Wanser opinion, on a finding of concurring negligence a proper construction of the agreement requires that the loss be equally borne. The appellant, invoking New York law, insists that it is entitled to complete indemnification because, it asserts, its negligence was passive; the appellee’s active. We think, however, that when the parties in clear and unequivocal language have called for an even division of a loss resulting from concurrent negligence, they are bound thereby and may not invoke law which, absent any agreement, would call for complete indemnity. This conclusion also is implicit in the Wanser opinion. But were it otherwise, we could not view the Railroad’s conduct in pushing the car ridden by the intestate past the post and its long-continued failure to cause a relocation of the post as negligence less active than that of the Lumber Company. This, too, is implicit in Wanser.
Lastly, the appellant insists that Deep Vein Coal Co. v. Chicago & E. I. Ry. Co., 7 Cir., 71 F.2d 963, and other cases which were distinguished in the Wanser opinion are applicable to this case. We disagree. The sidetrack agreement in the Deep Vein case, though containing similar phases, was vitally different in its textual structure; it specially called for complete indemnification for losses growing out of the location of structures in violation of the agreement. That was not the agreement here. And the other cases cited and distinguished in Wanser we think distinguishable also from the case before us.
Affirmed
. This same question was involved in Wanser v. Long Island Railroad Co., 2 Cir., 238 F.2d 467, certiorari denied Long Island R. Co. v. Central Islip Co-op. G. L. F. Service, 353 U.S. 911, 77 S.Ct. 668, 1 L.Ed.2d 665 in which this court implicitly gave the question an affirmative answer without mention of the jurisdictional point.
. A provision in the rule for impleading a third party who “is or may be liable to * * * the plaintiff” as well as the third-party plaintiff was eliminated by amendment made in 1946, effective in 1948.
. In Dewey v. West Fairmont Gas Coal Co., 123 U.S. 329, 8 S.Ct. 148, 31 L.Ed. 179, long before the emergence of the Federal Rules, it was so held.
. We think it implicit in the rationale of this opinion (1) that the court had ancillary jurisdiction of the third-party claim even though independent jurisdictional grounds were absent and (2) that but for the discretionary dismissal the ancillary jurisdicción of the third-party claim would have survived the adjudication of the main claim.
. This case much resembles that now on appeal in that after a settlement of the main claim before trial the court proceeded to adjudicate the third-party claim.
. “The Industry also agrees to indemnify and hold harmless the Rail Road Company for loss, damage, or injury from any act or omission of the Industry, its employees or agents, or any one not a party to this agreement using said side crack and switch connection, their employees or agents, to the person or property of the parties hereto and their employees, and to the person or property of any other person or corporation, while on or about said side track and switch connection; and if any claim or liability other than from fire shall arise from the joint or concurring negligence of both parties hereto, or the joint or concurring negligence of any one not a party to this agreement using said side track and switch connection and the Rail Road Company, it shall he borne equally by the Industry and the Rail Iioad Company.”