concurring.
I share the court’s opinion that the ’115 catalyst patent and the ’698 process patent do not claim the same invention, as this court and our predecessor court have defined “same invention”, and thus that “same invention double patenting” does not lie. I believe, however, that 35 U.S.C. § 1211 controls the result in this case, *358wherein the application for the ’698 patent was filed as result of a restriction requirement imposed by the Commissioner. Under these circumstances, the legal and policy arguments raised by Northern Petrochemical are not controlling of the issue: these arguments were answered by Congress when the statute was enacted.
Prior to the 1952 Patent Act, courts and patentees were aware of the unfairness that resulted when the Patent Office required restriction or division between claims in a patent application, thus requiring that a second patent application be carved out of the first, and then rejected the second application on the basis of the first. See In re Eisler, 203 F.2d 726, 97 USPQ 361 (CCPA 1953). Even if the patentee had objected to the restriction requirement, the rejection of the second application could be upheld, as in In re Kauffman, 152 F.2d 991, 68 USPQ 178 (CCPA 1946). And even when the Patent Office had required restriction and then had granted separate patents, courts had occasionally invalidated patents for double patenting. See, e.g., Remington Rand Business Service, Inc. v. Acme Card System Co., 71 F.2d 628, 22 USPQ 1 (4th Cir.), cert. denied, 293 U.S. 622, 55 S.Ct. 236, 79 L.Ed. 710 (1934).
The purpose of including § 121[3] in the 1952 Patent Act was to protect the patentee from the consequences of this PTO practice.2 The first printed text of this remedial legislation included the following provision:
If two or more patents are issued in consequence of a requirement for restriction under this section, no claim of any of said patents may be held invalid solely by reason of its inclusion in a separate patent.3
P.J. Federico’s accompanying Note stated that “[njeither of the resulting patents can be held invalid over the other merely because of their being divided in several patents.” 4 The Preliminary Draft also proposed to cut off the terminal portion of the second-issuing patent,5 but H.R. 9133, introduced by Representative Bryson, did not adopt the proposal that the later-issuing patent expire on the same date as the earlier patent. The revised text stated:
If two or more patents are issued in consequence of a requirement for restriction under this section, neither patent may be used as a reference against the other for the purpose of section 103 of this title____6
The next bill, H.R. 3760, included the courts as well as the Patent Office in its prohibition against use as a reference of a patent resulting from a requirement for restriction.7 The hearing record on H.R. 3760 contains the Report of the Laws and Rules Committee of the American Patent Law Association, which states that:
Section 121 gives statutory expression to division practice and specifically forbids the use of either the original or the division as a reference against the other____8
*359The hearing record also contains a letter from H.R. Hawgood of Cleveland to Representative Bryson, stating:
Section 121: In general, this seems to be a useful section, but the reference to the use of a parent or divisional case, against another is a bit ambiguous, particularly in the mention of section 103. Would it not be better to specify clearly that neither a parent nor divisional case could be used as a reference against the other for any purpose? 9
The phrase “for the purpose of section 103 of this title” was deleted from the section as enacted.
The Revision Note for § 121, in the House and Senate Reports accompanying the 1952 Patent Act, summarized the law as follows:
[Njeither of the resulting patents can be held invalid over the other merely because of their being divided in several patents.10
In “Commentary on New Title 35, U.S. Code ‘Patents’ ”, Charles J. Zinn, law revision counsel to the House Judiciary Committee’s Subcommittee No. 3 which was both the Subcommittee on Patents and the Subcommittee on Revision of the Laws, stated:
The Commissioner is given the discretion of requiring a division. The use of either the original or the division as a reference against the other is specifically forbidden____11
P.J. Federico advised the bar in 1951, at the time H.R. 9133 was introduced:
The intention of everybody involved is that double patenting is eliminated either in the application stage or in the patent stage____12
Since its enactment, the courts and the Patent Office have without significant exception upheld broadly the remedial purpose of 35 U.S.C. § 121. In 1963 Judge Rich discussed § 121 as follows:
To sum it up, the operation of the rule is that claims to inventions closely related to the invention claimed in the patent and not patentably distinguishable therefrom must be included in the same patent unless the applicant has been forced to make them in a separate application by a requirement of restriction, in which case section 121 of the statute acts to waive the rule.
In re Zickendraht, 319 F.2d 225, 232, 138 USPQ 22, 27 (CCPA 1963) (Rich, J., concurring). See also In re Schneller, 397 F.2d 350, 355, 158 USPQ 210, 215 (CCPA 1968), wherein Judge Rich wrote for the court: “Neither do we have any requirement of restriction, as provided in 35 U.S.C. 121, to excuse [double patenting].”
Practitioners have for decades relied on this provision, as discussed by the PTO Board of Appeals in Ex parte Nantz, 141 USPQ 523, 528 (Bd.App.1963):
The third sentence of this code section provides that neither the Patent Office nor the courts can use the patent issuing as a result of a requirement to divide against the still pending application. This provision of the third sentence would have meaning only if there has been an error in requiring restriction, since if the inventions between which restriction has been required are patent-ably different, the provision is not required, as shown by the case law. Only when there has been an error is it necessary to invoke the provision of the third sentence.
After the 1952 Patent Act, very few of the cases that raised questions of double patenting involved § 121. None of the cases discussed in the court’s opinion in the case at bar, i.e., Taylor, Wattes, Boylan, Vogel, or Carman, involved a PTO restric*360tion requirement. Those courts that discussed § 121 generally held that § 121[3] guards against invalidity based on double patenting if the division into more than one patent was due to a restriction requirement by the PTO. See, e.g., St. Regis Paper Co. v. Bemis Co., Inc., 403 F.Supp. 776, 787, 188 USPQ 107, 117 (S.D.Ill.1975), rev’d on other grounds, 549 F.2d 833, 193 USPQ 8 (7th Cir.), cert. denied, 434 U.S. 833, 98 S.Ct. 119, 54 L.Ed.2d 94, 195 USPQ 465 (1977) (“That procedure was in all respects in compliance with the provisions of 35 U.S.C. § 121. It must be presumed that the Examiner resolved any question of double patenting when he allowed the divisional application, absent clear and convincing proof to overcome that presumption.”); Illinois Tool Works, Inc. v. Foster Grant Co., Inc., 395 F.Supp. 234, 256, 181 USPQ 553, 569 (N.D.Ill.1974), aff'd, 547 F.2d 1300, 192 USPQ 365 (7th Cir.1976), cert. denied, 431 U.S. 929, 97 S.Ct. 2631, 53 L.Ed.2d 243, 194 USPQ 576 (1977) (“Under the statute (35 U.S.C. § 121), the claims of the two patents in suit must be considered with respect to each other in the same manner as one considers the claims of a single patent with respect to each other.”); Illinois Tool Works Inc. v. Solo Cup Co., 179 USPQ 322, 366 (N.D.I11.1973) (“The Patent Office did require restriction and consequently 35 U.S.C. 121 renders any double patenting inquiry moot____”); Union Carbide Corp. v. Dow Chemical Co., 619 F.Supp. 1036, 1059 (D.Del.1985) (“If it was Congress’ determination that the need to streamline the patenting process and remove some of the pitfalls that plagued patentees outweighed the disadvantage of permitting two like patents to coexist, it is not for the Court to second guess the wisdom of that determination.”).
These decisions demonstrate that from the practical viewpoint § 121 is particularly important when the restriction requirement is asserted to have been imposed in error, such that the court is asked to decide whether separate applications should have been required to have been filed. This is reinforced because of the limitation on appellate review of PTO restriction requirements. See In re Hengehold, 440 F.2d 1395, 1404, 169 USPQ 473, 480 (CCPA 1971) (“actions of examiners in requiring restriction under § 121 [are] within the supervision of the Commissioner and beyond the pale of review by the board”).
As a corollary, the safeguard of § 121[3] does not apply if the divisional application was voluntarily filed by the applicant and not in response to a PTO restriction requirement. In re Schneller, 397 F.2d 350, 354, 158 USPQ 210, 215 (CCPA 1968); In re Wright, 393 F.2d 1001, 1002 n. 1, 157 USPQ 519, 520 n. 1 (CCPA 1968). Nor does it apply if the restriction requirement was withdrawn by the examiner. In re Ziegler, 443 F.2d 1211, 1216, 170 USPQ 129, 132 (CCPA 1971).
The parties have not cited, and we have not found, any case wherein a court has invalidated, on the basis of double patenting, a patent filed as the result of a § 121 restriction requirement. Northern Petrochemical refers to Eversharp, Inc. v. Philip Morris Inc., 256 F.Supp. 778, 784, 150 USPQ 98, 103 (E.D.Va.1966), aff'd per curiam, 374 F.2d 511, 153 USPQ 91 (4th Cir.1967). In that case, however, the district court stated that “[t]he vice of plaintiff’s ’857 blade patent is not double patenting”, and invalidated the divisional patent on other grounds. In Pierce v. Hewlett-Packard Co., 220 F.2d 531, 533, 105 USPQ 50, 51-52 (1st Cir.), cert. denied, 350 U.S. 833, 76 S.Ct. 69, 100 L.Ed. 744, 107 USPQ 362 (1955), the court held that it was not bound by an incorrect restriction requirement, because “[plaintiff’s patent [was granted in] 1938. It was, therefore, impossible for the plaintiff’s patent to have been issued on an application which was required to be restricted under the 1952 act and consequently § 121 is inapplicable....”
Since the 1952 Patent Act, § 121 has protected patentees from the need to prove, before the PTO or the courts, that the claims of the divisional application are to an independent and distinct invention, when the patent examiner had determined during *361examination that the inventions were independent and distinct, and by requiring restriction had refused to examine the claims to any non-elected invention. The patent applicant thereafter had either to place the non-elected claims in a new patent application, or to abandon them. Section 121[3] effects a form of estoppel that shields the applicant from having to prove the correctness of the restriction requirement in order to preserve the validity of the second patent.
35 U.S.C. § 121 of course does not provide that multiple patents may be granted on the identical invention. To illustrate an identical invention, Vogel uses the hypothetical example of claims that differ only in the use of the expression 36 inches as opposed to 3 feet. But such theoretical bright lines do not make lawsuits. The variety of possible situations shown in the litigated cases on double patenting pays tribute to the wisdom of the legislators of § 121.
The Commissioner recognized the burden that § 121 placed on the PTO, and in section 804.01 of the Manual for Patent Examining Procedure (MPEP) (5th ed. 1983) the examiner is cautioned concerning the Office’s responsibility:
[Section 121’s] nullification of double patenting as a ground of rejection or invalidity in such cases imposes a heavy burden on the Office to guard against erroneous requirements for restriction where the claims define essentially the same inventions in different language and which, if acquiesced in, might result in the issuance of several patents for the same invention.
The deplorably long time between issuance of the two patents before us points up other systemic difficulties, but does not authorize the court to depart from the plain language and intent of § 121. As the court said in Illinois Tool Works Inc. v. Solo Cup Co., 179 USPQ at 364, “[t]o permit a double patenting attack on the ... patent is to completely emasculate 35 U.S.C. 121.”
. The first three sentences of 35 U.S.C. § 121 are:
If two or more independent and distinct inventions are claimed in one application, the Commissioner may require the application to be restricted to one of the inventions.
If the other invention is made the subject of a divisional application which complies with the requirements of section 120 of this title it shall be entitled to the benefit of the filing date of the original application.
A patent issuing on an application with respect to which a requirement for restriction under this section has been made, or on an application filed as a result of such a requirement, shall not be used as a reference either in the Patent and Trademark Office or in the *358courts against a divisional application or against the original application or any patent issued on either of them, if the divisional application is filed before the issuance of the patent on the other application.
. For detailed discussion see Walterscheid, Historical Development of the Law of Double Patenting Up Through the 1952 Patent Act, 4 A.P.L. A.QJ. 243, 260 (1976) (“double patenting prior to the Patent Act of 1952 constituted a massive, complex, confusing, and conflicting area of the patent law”).
. "Proposed Revision and Amendment of the Patent Laws”, characterized as a "Preliminary Draft with Notes” for the Committee on the Judiciary of the House of Representatives, at 21 (Comm. Print January 10, 1950).
. Id. at 22.
. Id. at 21.
. H.R. 9133, 81st Cong., 2d Sess. § 120 (1950).
. H.R. 3760, 82d Cong., 1st Sess. § 121 (1951).
. Hearings before Subcommittee No. 3 of the Committee on the Judiciary, House of Representatives, Eighty-Second Congress, First Session on H.R. 3760, 82d Cong., 1st Sess., Serial No. 9, at 45 (1951).
. Id. at 211.
. S.Rep. No. 1979, 82d Cong., 2d Sess. 20, reprinted in 1952 U.S.Code Cong. & Ad.News 2394, 2413; H.R.Rep. No. 1923, 82d Cong., 2d Sess. 20 (1952).
. 1952 U.S.Code Cong. & Ad.News 2507, 2515.
. Proceedings, Mid-Year Meeting, Section of Patent, Trademark, and Copyright Law, American Bar Association, held March 8-10, 1951, Shoreham Hotel, Wash., D.C., Vol. 1 at 257.