Case: 19-2015   Document: 68     Page: 1   Filed: 08/28/2020




   United States Court of Appeals
       for the Federal Circuit
                 ______________________

                    EGENERA, INC.,
                    Plaintiff-Appellant

                            v.

                CISCO SYSTEMS, INC.,
                   Defendant-Appellee
                 ______________________

                  2019-2015, 2019-2387
                 ______________________

     Appeals from the United States District Court for the
 District of Massachusetts in No. 1:16-cv-11613-RGS, Judge
 Richard G. Stearns.
                  ______________________

                Decided: August 28, 2020
                 ______________________

    DAN L. BAGATELL, Perkins Coie LLP, Hanover, NH, ar-
 gued for plaintiff-appellant. Also represented by ANDREW
 DUFRESNE, Madison, WI; MARTIN GILMORE, New York, NY;
 JOHN BRUCE CAMPBELL, JAMES ELROY QUIGLEY, JOEL
 LANCE THOLLANDER, McKool Smith, PC, Austin, TX;
 CHRISTOPHER THOR BOVENKAMP, Dallas, TX.

     E. JOSHUA ROSENKRANZ, Orrick, Herrington & Sutcliffe
 LLP, New York, NY, argued for defendant-appellee. Also
 represented by EDMUND HIRSCHFELD, DANIEL A. RUBENS;
 ELIZABETH MOULTON, Menlo Park, CA; MARK S. DAVIES,
 ETHAN P. FALLON, ANNE SAVIN, Washington, DC; BRIAN
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 2                        EGENERA, INC.   v. CISCO SYSTEMS, INC.



 LEARY, JONAS R. MCDAVIT, TAMIR PACKIN, Desmarais LLP,
 New York, NY.
                 ______________________

     Before PROST, Chief Judge, REYNA and STOLL, Circuit
                           Judges.
 PROST, Chief Judge.
     Egenera, Inc. (“Egenera”) sued Cisco Systems, Inc.
 (“Cisco”) in the United States District Court for the District
 of Massachusetts, alleging that Cisco’s enterprise server
 systems infringe various claims of U.S. Patent
 No. 7,231,430 (“the ’430 patent”).
     Prior to claim construction, and alongside an ongoing
 inter partes review (“IPR”) proceeding, Egenera separately
 petitioned the United States Patent and Trademark Office
 (“PTO”) to remove one of the eleven listed inventors from
 the ’430 patent. Following the district court’s claim con-
 struction and a trial on inventorship, Egenera asked the
 district court to add the removed inventor back to the pa-
 tent. The district court determined that judicial estoppel
 prevented Egenera from relisting the inventor and held the
 ’430 patent invalid for failing to name all inventors. See
 Egenera, Inc. v. Cisco Sys., Inc., 379 F. Supp. 3d 110
 (D. Mass. 2019) (“Invalidity Decision”); Egenera, Inc.
 v. Cisco Sys., Inc., 348 F. Supp. 3d 99 (D. Mass. 2019) (“Ju-
 dicial Estoppel Decision”); Egenera, Inc. v. Cisco Sys., Inc.,
 No. 16-11613, 2018 WL 717342 (D. Mass. Feb. 5, 2018)
 (“Claim Construction Decision”).
     Egenera appeals, challenging both the district court’s
 claim construction and the application of judicial estoppel.
 For the reasons described below, we affirm the district
 court’s claim construction but vacate the invalidity judg-
 ment based on judicial estoppel and remand for further
 proceedings.
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                       3



                          BACKGROUND
                                 I
     Egenera owns the ’430 patent, which claims a platform
 for automatically deploying a scalable and reconfigurable
 virtual network.
     In April 2001, Egenera filed a provisional application
 that resulted in four nonprovisional applications contain-
 ing the same specification. One of them resulted in the
 ’430 patent, covering the “overarching system architec-
 ture.” Appellant’s Br. 12.
      According to the ’430 patent’s specification, it is diffi-
 cult to anticipate the amount of computing power required
 in a large organization’s physical computer network, and
 manually upgrading or deploying new physical servers is
 slow and expensive. See generally ’430 patent col. 1
 ll. 21–61. To address this, the claimed system creates a
 quickly reconfigurable virtual network environment plat-
 form. The platform “provides a large pool of processors” for
 the virtual network to use. Id. at col. 2 ll. 47–52. A subset
 may be “selected and configured” to form a “virtualized net-
 work” (or, “processing area network”) to “serve a given set
 of applications or customer.” Id. Accordingly, “processing
 resources may be deployed rapidly and easily through soft-
 ware” instead of through physical reconfiguration. Id.
 at col. 2 ll. 57–62.
     Claim 1, which is representative, reads:
     1. A platform for automatically deploying at least
     one virtual processing area network, in response to
     software commands, said platform comprising:
     a plurality of computer processors connected to an
     internal communication network;
     at least one control node in communication with an
     external communication network and in communi-
     cation with an external storage network having an
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 4                        EGENERA, INC.   v. CISCO SYSTEMS, INC.



     external storage address space, wherein the at
     least one control node is connected to the internal
     communication network and thereby in communi-
     cation with the plurality of computer processors,
     said at least one control node including logic to re-
     ceive messages from the plurality of computer pro-
     cessors, wherein said received messages are
     addressed to the external communication network
     and to the external storage network and said at
     least one control node including logic to modify said
     received messages to transmit said modified mes-
     sages to the external communication network and to
     the external storage network;
     configuration logic for receiving and responding to
     said software commands, said software commands
     specifying (i) a number of processors for a virtual
     processing area network (ii) a virtual local area
     network topology defining interconnectivity and
     switching functionality among the specified proces-
     sors of the virtual processing area network, and
     (iii) a virtual storage space for the virtual pro-
     cessing area network, said configuration logic in-
     cluding logic to select, under programmatic control,
     a corresponding set of computer processors from
     the plurality of computer processors, to program
     said corresponding set of computer processors and
     the internal communication network to establish
     the specified virtual local area network topology,
     and to program the at least one control node to de-
     fine a virtual storage space for the virtual pro-
     cessing area network, said virtual storage space
     having a defined correspondence to a subset of the
     external storage address space of the external stor-
     age network; and
     wherein the plurality of computer processors and
     the at least one control node include network
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                        5



     emulation logic to emulate Ethernet functionality
     over the internal communication network.
 ’430 patent claim 1 (emphasis added).
     In this case, the construction of “logic to modify” is at
 issue in the context of “at least one control node . . . includ-
 ing logic to modify . . . received messages to transmit said
 modified messages to the external communication net-
 work.”
     Processors used by the virtual network may generate
 messages to be sent outside the network. But the outside
 network may use different protocols, see Invalidity Deci-
 sion, 379 F. Supp. 3d at 125, and so there must be a way to
 modify outbound messages so that those messages will be
 compatible with the external network. This is done by the
 “logic to modify” within the “control node.” See ’430 patent
 claim 1.
                                II
     Egenera sued Cisco in August 2016 for infringement of
 the ’430 patent. In response, Cisco filed an IPR petition
 challenging all eight of the patent’s claims.
     According to Egenera, upon reviewing the ’430 patent
 after Cisco’s IPR petition, it realized that all claim limita-
 tions had been conceived before one listed inventor, Mr. Pe-
 ter Schulter, had started working there. Appellant’s Br.
 18–19. Mr. Schulter had been hired by Egenera during the
 invention’s development for his “extensive networking ex-
 perience” and to “refine and code the networking subsys-
 tem” of the invention. Id. at 11; Invalidity Decision, 379 F.
 Supp. 3d at 118. And so, one month after responding to the
 IPR petition, Egenera separately petitioned the PTO to re-
 move Mr. Schulter as a listed inventor. Judicial Estoppel
 Decision, 348 F. Supp. 3d at 101; J.A. 9367–80. By then,
 Mr. Schulter, as well as most of the named inventors, no
 longer worked for Egenera. It is apparent that at least part
 of Egenera’s motivation to remove Mr. Schulter was to
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 6                        EGENERA, INC.   v. CISCO SYSTEMS, INC.



 facilitate swearing behind “Grosner,” a piece of prior art
 asserted against Egenera in the IPR. See Invalidity Deci-
 sion, 379 F. Supp. 3d at 114. Grosner’s priority date was
 November 2, 2000. Id. at 113. And Mr. Schulter joined
 Egenera on October 2, 2000. Id. at 112. But Egenera ar-
 gued an even-earlier conception date of September 29,
 2000. Id. at 114.
     While the inventorship petition was pending, the
 Board declined to institute Cisco’s IPR. J.A. 10912–28. In
 so doing, it assumed Grosner was prior art but neverthe-
 less concluded that Cisco had not met its burden of estab-
 lishing a reasonable likelihood of prevailing on the merits.
 J.A. 10922. Shortly thereafter, in January 2018, the PTO
 granted Egenera’s petition and removed Mr. Schulter’s
 name. J.A. 9387.
     Cisco had not argued that any of the “logic” terms
 should be interpreted as means-plus-function in the IPR,
 nor in its invalidity contentions.        E.g., J.A. 10368,
 12412–14. But it advanced a means-plus-function con-
 struction at the district court. And in February 2018, the
 district court issued an order construing the patent’s “logic”
 terms as means-plus-function elements. Claim Construc-
 tion Decision, 2018 WL 717342, at *1, *4–10. It concluded
 that the structure in the specification corresponding to the
 claimed function of the “logic to modify” was the so-called
 tripartite structure—the combination of a virtual LAN
 proxy, a physical LAN driver, and a virtual LAN server.
 Id. at *6–7; Invalidity Decision, 379 F. Supp. 3d at 128.
      Cisco next filed an amended answer in the district
 court asserting invalidity based on pre–America Invents
 Act (“AIA”) § 102(f)—contending that Mr. Schulter in-
 vented the tripartite structure, and therefore that the pa-
 tent did not list all inventors. J.A. 3238, 3251. In
 August 2018, Cisco moved for summary judgment of inva-
 lidity on this ground, which the district court denied, find-
 ing triable issues of fact regarding inventorship. Judicial
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                      7



 Estoppel Decision, 348 F. Supp. 3d at 108–09. But the court
 also rejected Egenera’s argument that if the trial showed
 Mr. Schulter to be an inventor, the patent’s inventorship
 should be corrected under 35 U.S.C. § 256(b).           Id.
 at 101–02. The court reasoned that judicial estoppel pre-
 cluded Egenera from “resurrect[ing]” Mr. Schulter’s inven-
 torship. Id. at 102.
     The court conducted a three-day bench trial on inven-
 torship. Invalidity Decision, 379 F. Supp. 3d at 112. The
 court found, in Cisco’s favor, that Mr. Schulter had con-
 ceived the tripartite structure. Id. at 125–29. The court
 then reiterated that Egenera was judicially estopped from
 invoking § 256 to restore Mr. Schulter’s name, thereby
 holding the ’430 patent invalid. Id. at 129.
     Egenera appealed the invalidity judgment, challenging
 the underlying construction of “logic to modify” and the ap-
 plication of judicial estoppel. We have jurisdiction under
 28 U.S.C. § 1295(a)(1).
                           DISCUSSION
                                 I
     First we address Egenera’s contention that the district
 court’s claim construction was wrong.
     At issue is the “logic to modify” limitation, which the
 district court construed as a means-plus-function element.
 For the reasons below, we agree with the district court’s
 claim construction.
     The ultimate interpretation of a patent claim is a legal
 question that we review de novo. Williamson v. Citrix
 Online, LLC, 792 F.3d 1339, 1346 (Fed. Cir. 2015) (citing
 Teva Pharm. USA, Inc. v. Sandoz, Inc., 574 U.S. 318,
 331–32 (2015)). To the extent the district court makes un-
 derlying findings of fact based on extrinsic evidence, we re-
 view them for clear error. Id.
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 8                        EGENERA, INC.   v. CISCO SYSTEMS, INC.



     Means-plus-function claiming occurs when a claim
 term invokes 35 U.S.C. § 112(f), 1 which states:
     An element in a claim for a combination may be ex-
     pressed as a means or step for performing a speci-
     fied function without the recital of structure,
     material, or acts in support thereof, and such claim
     shall be construed to cover the corresponding struc-
     ture, material, or acts described in the specification
     and equivalents thereof.
     We presume that claim terms with the word “means”
 invoke § 112(f) and that claim terms without the word
 “means” do not. Williamson, 792 F.3d at 1348 (en banc). 2
 This presumption, however, does not permit patentees to
 freely engage in functional claiming while circumventing
 § 112(f) simply by avoiding the word “means,” as we clari-
 fied in Williamson. See id. at 1349 (warning of “a prolifer-
 ation of functional claiming . . . free of the strictures set
 forth in the statute”). And so the presumption against
 means-plus-function interpretation is rebuttable if a chal-
 lenger demonstrates that a claim term either fails to “recite
 sufficiently definite structure” or recites “function without
 reciting sufficient structure for performing that function.”
 Id. (quoting Watts v. XL Sys., Inc., 232 F.3d 877, 880
 (Fed. Cir. 2000)).
     We clarified in Williamson that the presumption
 against means-plus-function claiming is not “strong” and
 that a challenger need not show that the limitation is “es-
 sentially . . . devoid of anything that can be construed as



     1   Although pre-AIA § 112, ¶ 6, applies in this case,
 the AIA recodified that provision as § 112(f). We use the
 AIA numbering for convenience.
    2    The discussion in Williamson of the applicability of
 § 112(f) was joined by the en banc court. 792 F.3d
 at 1347–49 & n.3.
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                       9



 structure.” Id. Rather, a challenger need only show that
 the structure is not “sufficient.” See id.; TEK Glob., S.R.L.
 v. Sealant Sys. Int’l, Inc., 920 F.3d 777, 785 (Fed. Cir.
 2019). For example, “[g]eneric terms such as ‘mechanism,’
 ‘element,’ ‘device,’ and other . . . verbal constructs may be
 used in a claim in a manner that is tantamount to using
 the word ‘means’ because they ‘typically do not connote suf-
 ficiently definite structure’ and therefore may invoke
 [§ 112(f)].” Williamson, 792 F.3d at 1350 (quoting Mass.
 Inst. of Tech. v. Abacus Software, 462 F.3d 1344, 1354
 (Fed. Cir. 2006)). Such terms may amount to “generic
 terms or black box recitations of structure or abstractions.”
 MTD Prods. v. Iancu, 933 F.3d 1336, 1341 (Fed. Cir. 2019)
 (quoting Zeroclick, LLC v. Apple Inc., 891 F.3d 1003, 1008
 (Fed. Cir. 2018)). Or a term may amount to a coined “nonce
 word”—that is, a word “invented . . . for one occasion only.”
 See Bryan A. Garner, Garner’s Modern English Usage 1016
 (4th ed. 2016); Webster’s Third New International Diction-
 ary (1961) (defining “nonce word” as “a word . . . coined and
 used apparently to suit one particular occasion . . . but not
 adopted into use generally”); Lighting World, Inc. v. Birch-
 wood Lighting, Inc., 382 F.3d 1354, 1360 (Fed. Cir. 2004)
 (noting that either a “generic structural term” or a “coined
 term” can invoke § 112(f)).
     If the presumption against means-plus-function inter-
 pretation is overcome, we must “identify the claimed func-
 tion” and then “determine what structure, if any, disclosed
 in the specification corresponds to the claimed function.”
 Williamson, 792 F.3d at 1351. These are questions of law,
 reviewed de novo. Kemco Sales, Inc. v. Control Papers Co.,
 208 F.3d 1352, 1360 (Fed. Cir. 2000).
    “To determine whether the claim limitation at issue
 connotes sufficiently definite structure to a person of ordi-
 nary skill in the art, we look first to intrinsic evidence, and
 then, if necessary, to the extrinsic evidence.” TEK Glob.,
 920 F.3d at 785 (citing Phillips v. AWH Corp., 415 F.3d
 1303 (Fed. Cir. 2005) (en banc)).
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 10                        EGENERA, INC.   v. CISCO SYSTEMS, INC.



                               A
     Egenera insists that the district court erred in constru-
 ing “logic to modify” as a means-plus-function limitation.
      The ’430 patent contains several “logic” terms. The dis-
 trict court construed them all as means-plus-function;
 Egenera challenges only the construction of “logic to modify
 said received messages to transmit said modified messages
 to the external communication network and to the external
 storage network.”
                               1
    The district court observed that, in the claim language,
 each “logic” term was “described by a specific function” and
 was unaccompanied by “structural components.” Claim
 Construction Decision, 2018 WL 717342, at *5.
      Examining the intrinsic evidence, the district court ex-
 plained that “[t]he specification discloses that ‘logic’ has to
 be implemented,” id. (citing ’430 patent col. 23 ll. 23–24,
 col. 25 ll. 3–4), and that such implemented logic could be
 “software logic” or “BIOS-based,” id. (citing ’430 patent
 col. 3 ll. 61, 63, col. 6 l. 18). The court concluded that the
 specification was then “consistent with an understanding
 of logic as an abstraction for the set of steps designed to
 accomplish a stated function.” Id.
      Egenera had argued that “logic” denotes “software,
 firmware, circuitry, or some combination thereof.” Id.
 at *4. The district court noted that Egenera’s favored def-
 inition was itself “so broad and formless as to be a generic
 black box for performing the recited computer-imple-
 mented functions.” Id. at *6 (cleaned up).
     Accordingly, the court concluded that the totality of the
 evidence rebutted the presumption against means-plus-
 function claiming.
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                      11



                                2
      On appeal, Egenera, pointing to its expert’s explana-
 tion and dictionary definitions, argues that “‘logic’ is a com-
 mon term of art meaning software, firmware, circuitry, or
 [a] combination thereof.” Appellant’s Br. 51. As Cisco ar-
 gues, “logic” as used in the claims means only a “general
 category of whatever may perform” the function. Appel-
 lee’s Br. 58, 62; cf. Williamson, 792 F.3d at 1350
 (“‘[M]odule’ is simply a generic description for software or
 hardware that performs a specified function.”).
     The question is not whether a claim term recites any
 structure but whether it recites sufficient structure—a
 claim term is subject to § 112(f) if it recites “function with-
 out reciting sufficient structure for performing that func-
 tion.” Williamson, 792 F.3d at 1348 (emphasis added)
 (quoting Watts, 232 F.3d at 880). Egenera does not explain
 how its “logic”—even assuming it connotes some possible
 structure in the general sense of software, firmware, or cir-
 cuitry—amounts to “sufficient structure for performing
 [the modification] function.” See id. (emphasis added).
      Egenera also argues that the “larger claim context” in-
 dicates that “logic” is structural because the “logic to mod-
 ify” is part of a supposedly structural component—the
 “control node.” Appellant’s Br. 52; Reply Br. 22. But that
 is not enough. Mere inclusion of a limitation within a
 structure does not automatically render the limitation it-
 self sufficiently structural. And, again, the question is not
 whether “logic” is utterly devoid of structure but whether
 the claim term recites sufficient structure to perform the
 claimed functions.
     Egenera next argues that the claim language defines
 the “inputs, outputs, connections, and operation” of the
 logic component. Appellant’s Br. 52–54 (citing Apple Inc.
 v. Motorola, Inc., 757 F.3d 1286, 1299–303 (Fed. Cir. 2014);
 Linear Tech. Corp. v. Impala Linear Corp., 379 F.3d 1311,
 1319–21 (Fed. Cir. 2004); Mass. Inst. of Tech., 462 F.3d
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 12                       EGENERA, INC.   v. CISCO SYSTEMS, INC.



 at 1355–56; and Lighting World, 382 F.3d at 1359–63); Re-
 ply Br. 23. But the cases Egenera cites do not compel its
 favored outcome and do not endorse black-box claiming.
 First, none of Egenera’s precedent considers Williamson.
 See Media Rights Techs., Inc. v. Capital One Fin. Corp.,
 800 F.3d 1366, 1373 (Fed. Cir. 2015) (cautioning against
 relying on pre-Williamson precedent). Second, in those
 cases the claim language and specification provided suffi-
 cient structure to the “inputs, outputs, connections, and op-
 eration” such that the pre-Williamson strong presumption
 against means-plus-function claiming was not overcome.
 E.g., Apple, 757 F.3d at 1303 (noting that because “the
 claim language and specification outline the rules that the
 [claim term] follow[s],” the written description places clear
 structural limitations on the claim term and so the “patent
 recites a claim term with a known meaning”). In contrast,
 here the claims and specification provide no structural lim-
 itation to the “inputs, outputs, connections, and operation”
 of the claimed “logic to modify.”
     We agree with Cisco: § 112(f) applies here. As used,
 “logic” is no more than a “black box recitation of structure”
 that is simply a generic substitute for “means.” See Wil-
 liamson, 792 F.3d at 1350. We therefore conclude that
 Cisco overcame the presumption against applying § 112(f).
                               B
     Egenera next argues that the district court identified
 the wrong structure as corresponding to the claimed func-
 tions of the “logic to modify” limitation.
     This limitation recites two functions: (1) “to modify said
 received messages to transmit said modified messages to
 the external communication network”; and (2) “to modify
 said received messages to transmit said modified mes-
 sages . . . to the external storage network.” See ’430 patent
 claim 1 (emphases added).
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                       13



     The district court concluded that the structure corre-
 sponding to the first function was “virtual LAN server 335,
 virtual LAN proxy 340, and physical LAN driver 345” and
 equivalents.    Claim Construction Decision, 2018 WL
 717342, at *7. The parties call this the “tripartite struc-
 ture.”
     Egenera now agues on appeal that the tripartite struc-
 ture is too broad. Appellant’s Br. 55–59. Within the tri-
 partite structure, insists Egenera, only the virtual LAN
 proxy “modifies outgoing messages.” Id. at 59. Cisco disa-
 grees, pointing to its expert’s testimony that the proxy does
 not “act in isolation” and “cannot perform the recited func-
 tion . . . by itself.” Appellee’s Br. 72 (citing J.A. 1431). Ra-
 ther, the LAN proxy is merely “the middleman.” Id. at 73.
 And, argues Cisco, Egenera cannot switch the scope of its
 claim construction on appeal.
     Egenera previously identified “control node 120” and
 equivalents as the corresponding structure when it argued
 at the district court.     Claim Construction Decision,
 2018 WL 717342, at *7. As Cisco highlights, this control
 node is a broad structure that itself encompasses the tri-
 partite structure. See Appellee’s Br. 70. Indeed, Egenera
 argued below that the tripartite structure was
 “overly[ ]narrow.” J.A. 3060.
     Now Egenera contends that the structure it objected to
 as overly narrow must be narrowed further. Egenera ex-
 plains that, below, its proposed structure corresponded to
 both claimed functions—i.e., not only messages to the “ex-
 ternal communication network” but also messages to the
 “external storage network.” Reply Br. at 24–26. We find
 unpersuasive this explanation for Egenera’s switch in
 scope, as Egenera fails to explain how subtracting the “ex-
 ternal storage network” portions from the “control node”
 leaves us with the ultra-narrow structure it advances
 newly on appeal.
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 14                       EGENERA, INC.   v. CISCO SYSTEMS, INC.



      We agree with Cisco that Egenera cannot now seek a
 much narrower construction on appeal. Digital-Vending
 Servs. Int’l, LLC v. Univ. of Phoenix, Inc., 672 F.3d 1270,
 1273 (Fed. Cir. 2012) (“[A] party may not, as a general rule,
 change the scope of its claim construction on appeal.”). At
 any rate, we also find the district court’s and Cisco’s rea-
 soning persuasive on the merits. The components of the
 tripartite structure—the virtual LAN server, virtual LAN
 proxy, and physical LAN driver—function in concert to
 modify messages to transmit to the external communica-
 tions network. See Claim Construction Decision, 2018 WL
 717342, at *7; ’430 patent col. 18 ll. 53–58, fig. 3B; Appel-
 lee’s Br. 72–74.
      Accordingly, we affirm the claim construction order.
                              II
     Next we turn to Egenera’s contention that the district
 court erred in applying judicial estoppel, thereby prevent-
 ing correction of inventorship and invalidating its patent
 as a consequence.
                              A
     First, we address whether Egenera could correct inven-
 torship, even absent judicial estoppel.
     The Constitution authorizes awarding patent exclusiv-
 ity only to an inventor. U.S. CONST. art. I, § 8, cl. 8. And
 so courts have historically held that if a patent does not
 reflect its true inventorship, it is invalid. See Pannu v.
 Iolab Corp., 155 F.3d 1344, 1349–50 (Fed. Cir. 1998) (col-
 lecting cases).
     Inventorship is sometimes easy to determine. But
 sometimes it is complicated, as with complex projects in-
 volving many contributors at various times. Ultimately,
 inventorship is a legal conclusion premised on underlying
 factual findings, and one that depends on claim construc-
 tion. In re VerHoef, 888 F.3d 1362, 1365 (Fed. Cir. 2018);
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                    15



 Trovan, Ltd. v. Sokymat SA, 299 F.3d 1292, 1302 (Fed. Cir.
 2002). And like validity, inventorship is a claim-by-claim
 question. Trovan, 299 F.3d at 1302. Accordingly, who
 should be listed on the face of a patent may vary depending
 on what, exactly, is claimed and what, exactly, a court de-
 termines the claim scope to be.
     The Patent Act allows a listing of inventors to be cor-
 rected either upon petition to the Director, see 35 U.S.C.
 § 256(a), or upon court order, see § 256(b). Our precedent
 recognizes that a patent cannot be invalidated if inventor-
 ship can be corrected instead. Pannu, 155 F.3d at 1350.
 The statutory text recognizes this too:
     The error of omitting inventors or naming persons
     who are not inventors shall not invalidate the pa-
     tent in which such error occurred if it can be cor-
     rected as provided in this section.
 35 U.S.C. § 256(b) (emphases added). Section 256 applies
 if “through error a person is named . . . as the inventor, or
 through error an inventor is not named.” § 256(a).
     As previously noted, the inventorship question in-
 volved Egenera’s attempt to add back an inventor,
 Mr. Schulter, who had previously been removed alongside
 the IPR. The district court declared in a footnote that
 Mr. Schulter’s removal by petition was therefore “a consid-
 ered act that is unlikely to qualify as an omission ‘through
 error.’” Judicial Estoppel Decision, 348 F. Supp. 3d
 at 102 n.1. Cisco agrees, arguing that Egenera’s petition
 was a “tactical ploy” rather than a “reasonable, but mis-
 taken, effort to get inventorship right.”         Appellee’s
 Br. 27–30 (arguing that “error” requires a “good-faith mis-
 take”). We note that although the district court declined to
 credit Egenera’s witnesses’ accounts of conception, it also
 declined to find inequitable conduct on these facts, despite
 being urged by Cisco to do so. See Judicial Estoppel Deci-
 sion, 348 F. Supp. 3d at 101; Invalidity Decision, 379 F.
 Supp. 3d at 129.
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 16                         EGENERA, INC.   v. CISCO SYSTEMS, INC.



      Our precedent provides that “error” in § 256 includes
 “all varieties of mistakes—honest and dishonest”—rather
 than only unintentional inaccuracy. Stark v. Advanced
 Magnetics, Inc., 119 F.3d 1551, 1554–56 (Fed. Cir. 1997). 3
 That is, Stark expressly construed “error” to “embrace
 more than simply honest mistakes.” Id. at 1554. Stark’s
 broad interpretation was intended to “harmonize[] well
 with the title 35 policy of seeking to reward the actual in-
 ventors of technological advances.” Id. Indeed, § 256 is a
 savings provision, functioning to prevent invalidation
 when correction is available. It is the inequitable-conduct
 rules that provide a safety valve in the event of deceit. Id.
 at 1555–56.
     Cisco invites us to sidestep Stark because the AIA has
 since amended § 256. Previously, § 256 contained an addi-
 tional requirement that the “error” of omitting an inventor
 occurred without “deceptive intention” on the inventor’s
 part. The scope of “error,” standing alone, was therefore



      3  Reissue under 35 U.S.C. § 251 also requires “error,”
 and our case law there is consistent with our case law on
 § 256. See, e.g., Fleming v. Escort Inc., 774 F.3d 1371, 1380
 (Fed. Cir. 2014) (“Errors are not limited to slips of the pen
 but encompass—and most often are—deliberate drafting
 choices. Not all choices qualify . . . .” (citation omitted)); id.
 (stating that error includes “deficient understandings” and
 choices that rest on “cognizable false or deficient under-
 standing of fact or law” but not simply a “now-regretted
 choice”); In re Dinsmore, 757 F.3d 1343, 1347–48 (Fed. Cir.
 2014); In re Rosuvastatin Calcium Pat. Litig., 703 F.3d 511,
 522–24 (Fed. Cir. 2012) (applying pre-AIA language and
 including deliberate actions) (collecting cases); In re Amos,
 953 F.2d 613, 616 (Fed. Cir. 1991) (noting that error in-
 cludes attorney’s mistake in understanding claim scope,
 “one of the most common sources of defects” (quoting In re
 Wilder, 736 F.2d 1516, 1519 (Fed. Cir. 1984)).
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                    17



 broad enough to otherwise include acts amounting to “de-
 ceptive intention”—that is, intentional inaccuracy. See
 Stark, 119 F.3d at 1554. With the AIA, “without . . . decep-
 tive intention” was struck from that section. See AIA, Pub.
 L. No. 112-29, § 20(f)(1)(B), 125 Stat. 284, 334 (2011). The
 essence of Cisco’s position is that when Congress removed
 this restrictive language that excluded intentional inaccu-
 racy in certain cases, it somehow narrowed the meaning of
 “error” to exclude intentional inaccuracy entirely. Appel-
 lee’s Br. 30. Cisco argues that Congress’s removal of this
 language was meant to harmonize “error” with what Cisco
 views as its plain meaning—one that excludes intentional
 inaccuracy. We had not yet addressed the impact of the
 AIA on the holding of Stark. See, e.g., CODA Dev. S.R.O.
 v. Goodyear Tire & Rubber Co., 916 F.3d 1350, 1358 n.6
 (Fed. Cir. 2019). But we now reject Cisco’s proposed inter-
 pretation because it is contrary to the text of § 256, the
 structure of the AIA, 4 and the AIA’s legislative history. 5
 We hold that the AIA did not narrow the meaning of


     4    For instance, through the AIA, deceptive-intention
 language was removed from the reissue provision,
 35 U.S.C. § 251, as well as the analogue of § 256 that ap-
 plies to patent applications, 35 U.S.C. § 116. See AIA
 § 20(a)(3)(B), (f)(1)(B), 125 Stat. at 333–34. The § 102(f)
 improper-inventorship invalidity provision was also re-
 moved. AIA § 3(b)(1), 125 Stat. at 285–86. And newly es-
 tablished derivation proceedings provide for correction of
 named inventors. AIA § 3(i), 125 Stat. at 289–90 (codified
 at 35 U.S.C. § 135(b)).
     5    See, e.g., 157 Cong. Rec. S1378 (daily ed. Mar. 8,
 2011) (statement of Sen. Kyl) (“Eliminating the various de-
 ceptive-intent requirements moves the U.S. patent system
 away from the 19th century model that focused on the pa-
 tent owner’s subjective intent, and towards a more objec-
 tive-evidence-based system that will be much cheaper to
 litigate and more efficient to administer.”).
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 18                       EGENERA, INC.   v. CISCO SYSTEMS, INC.



 “error.” Accordingly, § 256 does not exclude “considered
 acts,” or even “deceptive intention,” from the meaning of
 “error.” Cf. Judicial Estoppel Decision, 348 F. Supp. 3d at
 102 n.1. “Error” is simply the incorrect listing of inventors.
     Egenera asserted in its inventorship petition to the
 PTO, concurrent with the IPR, that Mr. Schulter was in-
 correctly listed as an inventor. At the time, no one had ar-
 gued that “logic to modify” was a means-plus-function
 term. Indeed, it presumptively was not. And Egenera op-
 posed such a construction when Cisco later advanced it;
 likewise, its position that Mr. Schulter was not an inventor
 was seemingly consistent with its preferred construction.
 But the court rejected Egenera’s construction in a way that
 also illuminated Mr. Schulter’s necessary presence as an
 inventor. After a three-day trial, and this appeal, the
 claim-construction and inventorship questions have at last
 been resolved. Because of these legal determinations, in
 retrospect, Egenera’s assertion in its inventorship petition
 was incorrect: Mr. Schulter was an inventor. According,
 we conclude that Mr. Schulter’s omission was “error.”
                               B
      Next we turn to judicial estoppel. 6 As noted, the dis-
 trict court here concluded that Egenera was judicially es-
 topped from adding Mr. Schulter’s name back to the patent
 after it held a trial establishing him to be an inventor—
 thereby invalidating the patent for improper inventorship.



      6   Cisco contends that Egenera waived any argument
 against judicial estoppel. Appellee’s Br. 31. Regardless,
 whether to apply the waiver rule is discretionary. Here,
 there has been complete briefing and argument on the ju-
 dicial estoppel issue. See Automated Merch. Sys., Inc.
 v. Lee, 782 F.3d 1376, 1379–80 (Fed. Cir. 2015). To apply
 waiver would not serve judicial economy or promote fair-
 ness, and so we address the merits.
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                       19



      As an initial matter, Egenera insists that judicial es-
 toppel can never prevent § 256 from saving a patent’s va-
 lidity. Appellant’s Br. 33–36; see Oral Arg. at 00:40–58,
 No. 19-2015,      http://oralarguments.cafc.uscourts.gov/de-
 fault.aspx?fl=19-2015.mp3. We need not decide that issue,
 however, because in this case the criteria for judicial estop-
 pel were not met.
      For questions of judicial estoppel, we apply the law of
 the regional circuit—here the First Circuit. Akamai
 Techs., Inc. v. Limelight Networks, Inc., 805 F.3d 1368,
 1374 (Fed. Cir. 2015). The legal effect of representations
 to the PTO and statutory interpretation of the Patent Act,
 however, are issues of Federal Circuit law. See Endo
 Pharm. Inc. v. Teva Pharm. USA, Inc., 919 F.3d 1347, 1352
 (Fed. Cir. 2019). Under First Circuit law, we review a dis-
 trict court’s application of judicial estoppel for abuse of dis-
 cretion. Akamai, 805 F.3d at 1374 (citing Knowlton
 v. Shaw, 704 F.3d 1, 9–10 (1st Cir. 2013)). We accept un-
 derlying findings of fact unless they are clearly erroneous
 and review the resolution of legal questions de novo. Id.
 The First Circuit “treat[s] a material mistake of law as a
 per se abuse of discretion.” Perry v. Blum, 629 F.3d 1, 8
 (1st Cir. 2010).
      Judicial estoppel is an equitable doctrine that prevents
 a litigant from taking a litigation position inconsistent with
 one successfully asserted in an earlier court proceeding.
 See id. “The purpose of the doctrine is to protect the integ-
 rity of the judicial process.” Id. Although the “contours of
 judicial estoppel are hazy,” and its application is case-de-
 pendent, the First Circuit applies the New Hampshire fac-
 tors. RFF Family P’ship v. Ross, 814 F.3d 520, 527–28
 (1st Cir. 2016) (Souter, J., sitting by designation). Accord-
 ingly, a court examines (1) whether a party’s earlier and
 later positions are “clearly inconsistent”—that is, “mutu-
 ally exclusive”; (2) whether the party “succeeded in per-
 suading a court to accept” the earlier position; and
 (3) whether the party would “derive an unfair advantage or
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 20                       EGENERA, INC.   v. CISCO SYSTEMS, INC.



 impose an unfair detriment” on the other side if not es-
 topped. New Hampshire v. Maine, 532 U.S. 742, 750–51
 (2001).
      We address the New Hampshire factors in turn.
                              1
     First, Egenera advanced no “clearly inconsistent” posi-
 tions.
     To be “clearly inconsistent,” positions must be “mutu-
 ally exclusive” and “directly inconsistent.” RFF, 814 F.3d
 at 528 (quoting Alt. Sys. Concepts, Inc. v. Synopsys, Inc.,
 374 F.3d 23, 33 (1st Cir. 2004)).
      In its § 256(a) petition, Egenera asked the PTO as a
 matter of formality “to delete Peter Schulter as an inventor
 of the invention being claimed.” J.A. 9367; see also
 37 C.F.R. § 1.324; MPEP § 1481.02 (9th ed. Rev 10.2019,
 June 2020). Cisco argues that the “clearly inconsistent po-
 sitions” were the two contrary uses of § 256. 7 See Oral Arg.
 at 19:05–25, 26:29–38. Here, of course, in light of the dis-
 trict court’s claim construction and accompanying inven-
 torship determination, Egenera is asking the district court
 to add Mr. Schulter back as an inventor. The district court
 concluded that “Egenera’s suggestion that Schulter may be
 relisted as an inventor as circumstances may dictate” was
 clearly inconsistent with its “September 2017 petition . . .
 that Schulter’s name was erroneously listed.” Judicial Es-
 toppel Decision, 348 F. Supp. 3d at 102. This was incorrect.




      7  If Cisco’s argument were accepted, it is hard to see
 how any inventorship correction could occur under § 256.
 By definition, a request to change inventorship would be
 inconsistent with the “position” taken at the outset of pros-
 ecution, in which inventor names are submitted with the
 application. And serial petitions would be impossible.
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                    21



     We do not think that multiple corrections under § 256
 are per se “mutually exclusive.” In any event, the district
 court’s intervening claim-construction and inventorship
 determinations further justify any seeming inconsistency.
 Cf. Biomedical Pat. Mgmt. Corp. v. Cal. Dep’t of Health
 Servs., 505 F.3d 1328, 1341–42 (Fed. Cir. 2007) (noting that
 “inconsistency” in the judicial estoppel context “is excused
 by an intervening change in the law”); see generally
 18B Wright & Miller, Federal Practice & Procedure
 § 4477.3 (2d ed., Apr. 2020 update).
     Inventorship, a complex legal conclusion, can depend
 on claim construction. Here, the underlying presumption
 was that Egenera’s claim terms, lacking “means,” were not
 means-plus-function. Egenera’s inventorship petition was
 consistent with that presumption. Indeed, it may well be
 that Mr. Schulter would not be an inventor under Egen-
 era’s preferred construction; but inventorship under that
 claim construction was not decided. And Egenera consist-
 ently protested the means-plus-function construction both
 at the district court and on appeal—a construction that the
 inventorship question was directly predicated on. There-
 fore, once those issues were decided, it was entirely con-
 sistent for Egenera to request an accompanying formal
 correction of inventorship. Accordingly, at least due to the
 intervening claim construction, it was not “mutually exclu-
 sive,” as judicial estoppel requires, to again request formal
 correction of inventorship.
     The district court thus erred in discerning “clearly in-
 consistent” positions.
                                2
     Second, Egenera did not succeed in persuading a court
 or court-like tribunal to accept its first position.
     “‘Acceptance’ in this context is a term of art.” Perry,
 629 F.3d at 11. That is, “a party need not show that the
 earlier representation led to a favorable ruling on the
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 22                       EGENERA, INC.   v. CISCO SYSTEMS, INC.



 merits . . . but must show that the court adopted and relied
 on the represented position either in a preliminary matter
 or as part of a final disposition.” Id. And “[t]he showing of
 judicial acceptance must be a strong one.” Id. In this fac-
 tor, we ask whether the earlier tribunal’s acceptance impli-
 cated the “truth-seeking function of the court.” Id. at 11
 (quoting Teledyne Indus., Inc. v. NLRB, 911 F.2d 1214,
 1218 (6th Cir. 1990)). This requirement aligns with the
 doctrine’s purpose of “safeguard[ing] the integrity of the
 courts by preventing parties from improperly manipulating
 the machinery of the judicial system.” New Hampshire,
 532 U.S. at 750.
      The district court concluded that “[t]he PTO accepted
 these representations”—referring to the inventorship peti-
 tion. Judicial Estoppel Decision, 348 F. Supp. 3d at 102.
 As an initial matter, the inventorship petition contained no
 underlying statements of fact—simply statements that
 Mr. Schulter’s listing was erroneous and that all the co-
 listed inventors agreed or did not disagree. See J.A.
 9367–80. The PTO did not cast these statements into the
 crucible of examination. Rather, it agreed that all the sig-
 natures and fees were in order. See J.A. 9388; MPEP
 § 1481.02.
     Egenera contends that its statements in its petition
 “did not involve the judicial process necessary for judicial
 estoppel.” Appellant’s Br. 42. Instead, the § 256 petition
 process is “ministerial” and “does not involve any tribunal,
 judicial officer, or substantive analysis.” Id. Cisco replies
 that Egenera undisputedly “persuaded” the PTO that
 “Schulter was not an inventor.” Appellee’s Br. 44.
     Under 37 C.F.R. § 1.324(b), the PTO examines a re-
 quest only for the presence of supporting statements and
 the required fee. See also MPEP § 1481.02; J.A. 9388. No
 substantive examination occurs, and the PTO does not con-
 sider the substantive adequacy of the petition. Cisco ar-
 gues that the First Circuit has rejected a “ministerial”
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                       23



 exception. But in explanation, Cisco points out that unex-
 amined identification of assets during bankruptcy proceed-
 ings can ground judicial estoppel in a later bankruptcy
 proceeding. See Appellee’s Br. 45 (citing Guay v. Burack,
 677 F.3d 10, 17 (1st Cir. 2012)). We find Cisco’s arguments
 unpersuasive: bankruptcy schedules occur in the context of
 a bankruptcy court—they are specific representations of
 fact before a tribunal. 8 And as Egenera argues, Cisco’s
 chosen administrative judicial-estoppel precedents involve
 “inconsistent statements about an objective fact, such as
 the existence of bankruptcy assets or a claimed disability”
 rather than “context-related legal conclusions.” Reply Br.
 19. 9
     Accordingly, even though we agree that judicial estop-
 pel can occur in an administrative tribunal, 10 we disagree
 that a § 256 petition, without more, counts as “persuasion”
 of a “court” for judicial-estoppel purposes.




    8     Cisco also points to out-of-circuit applications of ju-
 dicial estoppel related to the Social Security Administra-
 tion’s acceptance of statements in a disability-insurance
 application. See Appellee’s Br. 46 n.3. Again, those cases
 are not only not binding but also unpersuasive, as they in-
 volve inconsistent statements about objective facts.
     9    “[J]udicial estoppel arises only from a position
 taken in an adjudicatory proceeding. Inconsistent positions
 taken in other contexts must be measured by other theo-
 ries.” Federal Practice & Procedure § 4477; see also id.
 § 4477.2 (“A position asserted before a government official
 in nonadjudicatory proceedings . . . should not support ‘ju-
 dicial’ estoppel.”).
     10   See Trs. v. United States, 593 F.3d 1346, 1354 (Fed.
 Cir. 2010) (“Judicial estoppel applies just as much when
 one of the tribunals is an administrative agency as it does
 when both tribunals are courts.” (emphasis added)).
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 24                       EGENERA, INC.   v. CISCO SYSTEMS, INC.



     This determination is narrow. We do not hold that ju-
 dicial estoppel cannot apply to statements made during
 substantive prosecution, ex parte reexamination, or other
 quasi-adjudicatory proceedings—an issue not before us.
 And we do not go so far as to say that other theories of es-
 toppel cannot apply to ministerial filings or representa-
 tions before the PTO. But judicial estoppel cannot be
 stretched beyond persuading a tribunal, and it does not ap-
 ply here.
                               3
     Third, Egenera would gain no unfair advantage, and
 Cisco would suffer no unfair prejudice, if judicial estoppel
 were not applied.
     The focus of this inquiry is on whether not applying es-
 toppel would result in unfair advantage or prejudice. See
 New Hampshire, 532 U.S. at 751 (“[Courts ask] whether
 the party seeking to assert an inconsistent position would
 derive an unfair advantage . . . if not estopped.”); RFF,
 814 F.3d at 528.
      Egenera argues that it would obtain no unfair ad-
 vantage by correcting inventorship in conformance with
 the district court’s inventorship determination. Appel-
 lant’s Br. 45–46. The petition was not granted until after
 the Board denied institution of the IPR on the merits.
 Egenera points out that the petition did not affect the IPR,
 and correction would simply “foster resolution of this case
 on the merits.” Appellant’s Br. 45–46. Cisco responds that,
 as the district court noted, Egenera’s disavowal of
 Mr. Schulter’s inventorship enabled it to argue for an ear-
 lier priority date to bolster its IPR and litigation position.
 Appellee’s Br. 47; Judicial Estoppel Decision, 348 F.
 Supp. 3d at 101–02. But in any event, it ended up not mak-
 ing a difference. The Board considered Cisco’s prior art
 without addressing Egenera’s priority arguments. And
 Cisco fails to explain how, even if there would be an
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 EGENERA, INC.   v. CISCO SYSTEMS, INC.                      25



 advantage conferred on Egenera by failure to estop, that
 advantage would be “unfair” under these facts.
     Things might be different had Egenera succeeded in
 swearing behind the prior art. We do not go so far as to
 declare that there would be no potential for judicial estop-
 pel had the Board fully considered and adopted Egenera’s
 swearing-behind arguments. But that would be estoppel
 on the basis of a prior representation to a tribunal (i.e., the
 Board). And both prejudice and inconsistency would be
 clear: there would be the potential of two judicial decisions
 predicated on opposite inventorship statuses. But that is
 not this case. Here, there would be no unfair prejudice in
 refusing to estop. The district court did not identify any.
 See Judicial Estoppel Decision, 348 F. Supp. 3d at 101–02.
 Cisco identified none in its brief, nor when pressed at oral
 argument. See Oral Arg. at 15:30–17:34.
      Cisco dismisses this prong of the New Hampshire fac-
 tors as purely optional under First Circuit law, arguing
 only that it is “enough that Egenera took ‘contradictory’ po-
 sitions ‘in search of legal advantage.’” Appellee’s Br. 47,
 49–50 (citing Alt. Sys. Concepts, 374 F.3d at 33). We disa-
 gree with Cisco’s reading of Alternative System Concepts,
 which would collapse the first and third prongs into one.
 And we decline to ignore abundant First Circuit precedent
 signifying the importance of this factor. E.g., RFF,
 814 F.3d at 528; Perry, 629 F.3d at 8–9.
      Accordingly, there would be no unfair advantage or un-
 fair prejudice in refusing to estop Egenera.
                                4
     The district court legally erred as to each New Hamp-
 shire factor. We therefore hold that the district court
 abused its discretion by applying judicial estoppel.
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 26                        EGENERA, INC.   v. CISCO SYSTEMS, INC.



                          CONCLUSION
      We have considered the parties’ remaining arguments
 but find them unpersuasive. For the foregoing reasons, we
 affirm the district court’s claim construction but vacate the
 district court’s invalidity judgment and the accompanying
 cost award. We remand for further proceedings.
      AFFIRMED-IN-PART, VACATED-IN-PART, AND
                    REMANDED
                             COSTS
       The parties shall bear their own costs.
