delivered the opinion of the Court.

The Government brought this civil action to enjoin the International Salt Company, appellant here, from carrying out provisions of the leases of its patented machines to the effect that lessees would use therein only International’s salt products. The restriction is alleged to violate § 1 of the Sherman Act,^[1] and § 3 of the Clayton Act.^[2] Upon appellant’s answer and admissions of fact, the Government moved for summary judgment under Rule 56 of the Rules of Civil Procedure, upon the ground that no issue as to a material fact was presented and[*394] that, on the admissions, judgment followed as matter of law. Neither party submitted affidavits. Judgment was granted^[3] and appeal was taken directly to this Court.^[4]

It was established by pleadings or admissions that the International Salt Company is engaged in interstate commerce in salt, of which it is the country’s largest producer for industrial uses. It also owns patents on two machines for utilization of salt products. One, the “Lixator,” dissolves rock salt into a brine used in various industrial processes. The other, the “Saltomat,” injects salt, in tablet form, into canned products during the canning process. The principal distribution of each of these machines is under leases which, among other things, require the lessees to purchase from appellant all unpatented salt and salt tablets consumed in the leased machines.

Appellant had outstanding 790 leases of an equal number of “Lixators,” all of which leases were on appellant’s standard form containing the tying clause^[5] and other[*395] standard provisions; of 50 other leases which somewhat varied the terms, all but 4 contained the tying clause. It also had in effect 73 leases of 96 “Saltomats,” all containing the restrictive clause.^[6] In 1944, appellant sold approximately 119,000 tons of salt, for about $500,000, for use in these machines.

The appellant’s patents confer a limited monopoly of the invention they reward. From them appellant derives a right to restrain others from making, vending or using the patented machines. But the patents confer no right[*396] to restrain use of, or trade in, unpatented salt. By contracting to close this market for salt against competition, International has engaged in a restraint of trade for which its patents afford no immunity from the antitrust laws. Morton Salt Co. v. G. S. Suppiger Co., 314 U. S. 488; Mercoid Corp. v. Mid-Continent Investment Co., 320 U. S. 661; Mercoid Corp. v. Minneapolis-Honey well Co., 320 U. S. 680.

Appellant contends, however, that summary judgment was unauthorized because it precluded trial of alleged issues of fact as to whether the restraint was unreasonable within the Sherman Act or substantially lessened competition or tended to create a monopoly in salt within the Clayton Act. We think the admitted facts left no genuine issue. Not only is price-fixing unreasonable, per se, United States v. Socony-Vacuum Oil Co., 310 U. S. 150; United States v. Trenton Potteries Co., 273 U. S. 392, but also it is unreasonable, per se, to foreclose competitors from any substantial market. Fashion Originators Guild v. Federal Trade Commission, 114 F. 2d 80, affirmed, 312 U. S. 457. The volume of business affected by these contracts cannot be said to be insignificant or insubstantial and the tendency of the arrangement to accomplishment of monopoly seems obvious. Under the law, agreements are forbidden which “tend to create a monopoly,” and it is immaterial that the tendency is a creeping one rather than one that proceeds at full gallop; nor does the law await arrival at the goal before condemning the direction of the movement.

Appellant contends, however, that the “Lixator” contracts are saved from unreasonableness and from the tendency to monopoly because they provided that if any competitor offered salt of equal grade at a lower price, the lessee should be free to buy in the open market, unless appellant would furnish the salt at an equal price; and[*397] the “Saltomat” agreements provided that the lessee was entitled to the benefit of any general price reduction in lessor’s salt tablets. The “Lixator” provision does, of course, afford a measure of protection to the lessee, but it does not avoid the stifling effect of the agreement on competition. The appellant had at all times a priority on the business at equal prices. A competitor would have to undercut appellant’s price to have any hope of capturing the market, while appellant could hold that market by merely meeting competition. We do not think this concession relieves the contract of being a restraint of trade, albeit a less harsh one than would result in the absence of such a provision. The “Saltomat” provision obviously has no effect of legal significance since it gives the lessee nothing more than a right to buy appellant’s salt tablets at appellant’s going price. All purchases must in any event be of appellant’s product.

Appellant also urges that since under the leases it remained under an obligation to repair and maintain the machines, it was reasonable to confine their use to its own salt because its high quality assured satisfactory functioning and low maintenance cost. The appellant’s rock salt is alleged to have an average sodium chloride content of 98.2%. Rock salt of other producers, it is said, “does not run consistent in sodium chloride content and in many instances runs as low as 95% of sodium chloride.” This greater percentage of insoluble impurities allegedly disturbs the functioning of the “Lixator” machine. A somewhat similar claim is pleaded as to the “Saltomat.”

Of course, a lessor may impose on a lessee reasonable restrictions designed in good faith to minimize maintenance burdens and to assure satisfactory operation. We may assume, as matter of argument, that if the “Lixator” functions best on rock salt of average sodium chloride content of 98.2%, the lessee might be required to use[*398] only salt meeting such a specification of quality. But it is not pleaded, nor is it argued, that the machine is allergic to salt of equal quality produced by anyone except International. If others cannot produce salt equal to reasonable specifications for machine use, it is one thing; but it is admitted that, at times, at least, competitors do offer such a product. They are, however, shut out of the market by a provision that limits it, not in terms of quality, but in terms of a particular vendor. Rules for use of leased machinery must not be disguised restraints of free competition, though they may set reasonable standards which all suppliers must meet. Cf. International Business Machines Corp. v. United States, 298 U. S. 131.

Appellant urges other objections to the summary judgment. The tying clause has not been insisted upon in all leases, nor has it always been enforced when it was included. But these facts do not justify the general use of the restriction which has been admitted here.

The appellant also strongly objects to the provisions of the sixth paragraph of the decree.^[7] Appellant denies[*399] the necessity for such provision and it is true that the record discloses no threat to discriminate after the judgment of the court is pronounced. It also suggests that we modify the judgment to accept a proposed alternative provision^[8] similar to one it says it urged upon the District Court, which rejected it. The record does not show what proceedings were had between rendering of the court’s opinion and signing of the decree.

The specific ground of objection raised by appellant to paragraph sixth is that International may find it necessary in some sections of the country to reduce the rental rates of the machines in order that its machines may compete with those of others. Of course, the Clayton Act itself^[9] permits one charged with price discrimination to show that he lowered his price in good faith to meet competition. Obviously, the District Court was not intending to prevent competition or to disable the appellant from meeting or offering it. The Government, too, says it would not oppose permitting a lower price to meet, in good faith, the equally low price of a competitor if the need arose.

[*400] The short of the contention is that since the company never has threatened to violate any decree entered in this case to restrain future use of the illegal leases, it feels that the provision invalidating the objectionable leases should end the matter and that, as to any additional provisions, appellant is entitled to stand before the court in the same position as one who has never violated the law at all — that the injunction should go no farther than the violation or threat of violation. We cannot agree that the consequences of proved violations are so limited. The fact is established that the appellant already has wedged itself into this salt market by methods forbidden by law. The District Court is not obliged to assume, contrary to common experience, that a violator of the antitrust laws will relinquish the fruits of his violation more completely than the court requires him to do. And advantages already in hand may be held by methods more subtle and informed, and more difficult to prove, than those which, in the first place, win a market. When the purpose to restrain trade appears from a clear violation of law, it is not necessary that all of the untraveled roads to that end be left open and that only the worn one be closed. The usual ways to the prohibited goal may be blocked against the proven transgressor and the burden put upon him to bring any proper claims for relief to the court’s attention. And it is desirable, in the interests of the court and of both litigants, that the decree be as specific as possible, not only in the core of its relief, but in its outward limits, so that parties may know their duties and unintended contempts may not occur.

The framing of decrees should take place in the District rather than in Appellate Courts.^[10] They are invested[*401] with large discretion to model their judgments to fit the exigencies of the particular case. United States v. Crescent Amusement Co., 323 U. S. 173, 185; United States v. National Lead Co., 332 U. S. 319. In an equity suit, the end to be served is not punishment of past transgression, nor is it merely to end specific illegal practices. A public interest served by such civil suits is that they effectively pry open to competition a market that has been closed by defendants’ illegal restraints. If this decree accomplishes less than that, the Government has won a lawsuit and lost a cause.

The District Court has retained jurisdiction, by the terms of its judgment, for the purpose of “enabling any of the parties ... to apply to the court at any time for such further orders and directions as may be necessary or appropriate for the construction or carrying out of this judgment” and “for the amendment, modifications or termination of any of the provisions . . . .” We think it would not be good judicial administration to strike paragraph VI from the judgment to meet a hypothetical situation when the District Court has purposely left the way open to remedy any such situations if and when the need arises. The factual basis of the claim for modification should appear in evidentiary form before the District Court rather than in the argumentative form in which it is before us. Nor are we impressed that this will require a multitude of separate applications. Once the concrete problem is before the District Court it will no doubt be able to fashion a provision that will avoid repetitious applications which would be as vexatious to the Court as to the litigants. We leave the appellant to proper appli[*402]cation to the court below and deny the relief here, upon the present state of the record, without prejudice.

Judgment affirmed.