. . . Indeed, the doctrine was established to fulfill a purpose related to, but distinct from, claim preclusion. . . .
Introduction
In Wisconsin Alumni Research Foundation v. Apple Inc., Nos. 2022-1884, 2022-1886 (Fed. Cir. Aug. 28, 2024) (“Decision”), the United States Court of Appeals for the Federal Circuit considered the preclusive effect of its prior ruling in an appeal of the first of two patent infringement lawsuits brought by WARF against Apple. In that first case, WARF I, a jury found that Apple’s A7 and A8 processors used in Apple’s iPhone and iPad products literally infringed WARF’s U.S. Patent No. 5,781,752 (“the ’752 patent”). However, on appeal, the Federal Circuit reversed the jury’s verdict of literal infringement. See Wis. Alumni Rsch. Found. v. Apple Inc., 905 F.3d 1341 (Fed. Cir. 2018). The Federal Circuit’s reversal of the jury’s verdict led to a prolonged legal battle in the district court over whether WARF could further pursue its infringement claims under the doctrine of equivalents against the same A7 and A8 processors in a new trial in WARF I, and against Apple’s next-generation A9 and A10 processors in the second lawsuit, WARF II.
The district court ultimately ruled that WARF had waived its doctrine of equivalents theory of infringement in WARF I against Apple’s A7 and A8 processors and that the Federal Circuit’s reversal of the jury’s verdict in WARF I precluded WARF’s claims against Apple’s A9 and A10 processors in WARF II. The district court therefore entered judgment in favor of Apple in both cases. In this second appeal, the Federal Circuit addressed three key issues in affirming the district court’s rulings: WARF’s waiver of the doctrine of equivalents, application of issue preclusion, and, notably, application of the so-called “Kessler doctrine.” Originating in an early U.S. Supreme Court decision, Kessler v. Eldred, 206 U.S. 285 (1907), the Kessler doctrine is a rarely invoked rule that prevents repeated litigation against the same product following a judgment of non-infringement, even when later litigation is brought against a different accused infringer, for example, a manufacturer’s customer.
The Parties & the Patent
WARF manages the intellectual property arising from research conducted at the University of Wisconsin-Madison. For decades, WARF has played a significant role in both securing patents on behalf of the university and enforcing those patents against entities that allegedly use the claimed technologies without authorization. Apple is a well-known manufacturer of computer and smartphone products.
The ’752 patent, titled Table-Based Data Speculation Circuit for Parallel Processing Computers, was filed in December 1996 and issued in July 1998. The patent claims a method that improves the speed of computer processors by enabling the execution of software instructions using a “predictor circuit.” This predictor circuit identifies certain dependencies among instructions in the software program and predicts whether a given instruction can be executed out of sequence without causing errors—effectively making educated guesses about whether the instruction depends on data from earlier rather than later instructions. By accurately predicting which instructions can be executed in parallel, the predictor circuit increases processing efficiency and reduces delays. WARF alleged that the functions performed by the “Load-Store Dependency (LSD) Predictors” in Apple’s processors infringed the ’752 patent’s claims.
Procedural Background: A Decade of Litigation
WARF filed its first suit against Apple in January 2014, accusing Apple’s A7 and A8 processors of infringing the ’752 patent. In September 2015, the district court conducted a jury trial to resolve the parties' dispute about literal infringement and the disputed claim term, “particular,” appearing in the ’752 patent’s claims. WARF’s case hinged on that claim term because all asserted patent claims required the predictor circuit to generate a prediction associated with a “particular” load instruction. Neither party had asked the court to interpret the meaning of “particular” as used in the claims, leaving its interpretation for the parties to dispute at trial. Decision at 7.
During trial, Apple contended that “particular” referred to a single instruction, not a group of instructions, and therefore argued that because its processors referenced groups of instructions in parallel, they could not literally infringe the patent’s claims. Ultimately, the jury rejected Apple's argument and found that Apple’s A7 and A8 processors literally infringed the patent, and the district court denied Apple’s post-trial motions to set aside the jury’s verdict. Apple appealed, and in 2018, the Federal Circuit reversed the jury’s verdict, ruling that the plain meaning of “particular,” required the prediction to be associated with only one instruction, not a group of instructions. Decision at 4-7.
Shortly before trial commenced in WARF I, WARF filed a second lawsuit against Apple in 2015, referred to in the Decision as WARF II, accusing Apple’s A9 and A10 processors of infringing the same patent claims. The district court stayed this second case during the appeal of WARF I, recognizing that the outcome of the first case would likely impact the second case. After the Federal Circuit’s reversal in WARF I, WARF abandoned its theory of literal infringement against the A9 and A10 processors. Instead, WARF sought to assert its patent claims under the doctrine of equivalents in WARF II against the A9 and A10 processors and likewise sought to reassert its claims under the doctrine of equivalents against the A7 and A8 processors in a new trial in WARF I. Decision at 8-11.
The district court rejected WARF’s attempt to revive its claims, finding that WARF waived its right to assert the doctrine of equivalents against the A7 and A8 processors in WARF I. The district court further held that WARF’s claims against the A9 and A10 processors in WARF II were barred by issue preclusion and the Kessler doctrine based on the outcome of WARF I. The district court entered final judgment in both WARF I and WARF II in favor of Apple. Decision at 11. WARF appealed both judgments to the Federal Circuit.
The Federal Circuit’s Analysis
Issue 1: Waiver of the Doctrine of Equivalents
The doctrine of equivalents allows a patent holder to prove infringement even when the accused product does not literally meet the precise wording of a patent claim, as long as the product performs substantially the same function in substantially the same way to achieve the same result. See generally, Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605 (1950). Initially, WARF sought to rely on both literal infringement and the doctrine of equivalents in WARF I to prove that Apple’s A7 and A8 processors infringed the ’752 patent. However, shortly before trial, WARF made a strategic decision to drop its doctrine of equivalents theory of infringement in exchange for Apple’s agreement to withhold certain evidence related to its own patents. As a result, WARF proceeded to trial solely on a theory of literal infringement. Decision at 6.
Before reaching the issue of waiver, the Federal Circuit addressed WARF’s argument that the court’s 2018 appellate decision materially altered the construction of the term “particular” in a such way that excused WARF’s decision to drop the doctrine of equivalents. WARF essentially argued that had it known the court’s ultimate construction of “particular,” it would not have agreed to abandon its theory of infringement under the doctrine of equivalents. The Federal Circuit rejected that argument, noting that its construction of “particular” was not materially different from the construction urged by Apple when WARF agreed to forego the doctrine of equivalents before trial. Decision at 14.
Undaunted, WARF argued that its situation was nevertheless analogous to that of the patentee in Exxon Chemical Patents, Inc. v. Lubrizol Corp., 137 F.3d 1475 (Fed. Cir. 1998). There, the patentee, Exxon, asserted both literal infringement and infringement under the doctrine of equivalents during its presentation of evidence at trial. However, the doctrine of equivalents became moot after the close of evidence when the district court narrowly construed the patent claims and instructed the jury on literal infringement only. Despite the jury's ultimate verdict of literal infringement in favor of Exxon, the Federal Circuit overturned the verdict on appeal by construing the claims in a manner that ruled out literal infringement. In a subsequent appeal, Exxon, 137 F.3d at 1457, the Federal Circuit ruled that its mandate in the first appeal incorporating the new claim construction did not preclude a new trial on the doctrine of equivalents because the district court’s claim construction ruling during trial prevented Exxon from presenting that theory to the jury.
WARF thus argued that, like Exxon, it should be entitled to a new trial in WARF I on the doctrine of equivalents due to the Federal Circuit’s reversal of the jury’s verdict of literal infringement. The Federal Circuit, however, distinguished Exxon on several grounds. Unlike Exxon, where the doctrine of equivalents was ultimately mooted during trial after the district court’s claim construction ruling, WARF voluntarily abandoned the doctrine of equivalents before trial had even begun. The district court in WARF I therefore did not preclude WARF from presenting its doctrine of equivalents case to the jury—it was WARF’s own strategic choice. Thus, when the Federal Circuit reversed the literal infringement ruling in WARF I, its mandate pertained solely to the literal infringement issue presented during the trial. The mandate therefore did not authorize the district court to conduct a second trial on the doctrine of equivalents, which WARF had not pursued during trial. Decision at 11-13.
Finally, the Federal Circuit affirmed the district court’s ruling that WARF waived its right to assert the doctrine of equivalents. The court was satisfied that WARF’s decision to forego the doctrine of equivalents before trial, in exchange for Apple’s agreement to forego its presentation of certain evidence, was a deliberate strategic choice that amounted to a waiver. Decision at 12-15 (citing United States v. Hible, 700 F.3d 958, 961 (7th Cir. 2012) (waiver arises when a party “for strategic reasons elects to pursue one argument while foregoing another”); Boss Control, Inc. v. Bombardier Inc., 410 F.3d 1372, 1380 (Fed. Cir. 2005) (“[F]ail[ing] to present substantive arguments to the district court concerning infringement under the doctrine of equivalents” constitutes a waiver of the issue)). The court thus emphasized that WARF's choice to abandon the doctrine of equivalents before trial could not later be undone when the case did not proceed in its favor. Decision at 16-17. The Federal Circuit, therefore, concluded that the district court properly denied WARF’s motion for a new trial against Apple’s A7 and A8 processors under the doctrine of equivalents. Id. at 20.
Issue 2: Issue Preclusion
The Federal Circuit also affirmed the district court’s application of “issue preclusion” that barred WARF from pursuing infringement claims under the doctrine of equivalents against Apple’s later-developed A9 and A10 processors in WARF II. In doing so, the Federal Circuit explained how its prior ruling in WARF I that the A7 and A8 processors did not literally infringe the ’752 patent precluded WARF’s claims in WARF II, even though the subsequent litigation involved different products and a different theory of infringement.
Issue preclusion, also known as collateral estoppel, prevents a party from relitigating an issue that was already decided in a prior case. For issue preclusion to apply, four elements must be met: (1) the issue must be identical to one involved in a prior action; (2) the issue must have been actually litigated; (3) the issue’s determination must have been essential to the final judgment; and (4) the party against whom estoppel is invoked must have been represented in the prior action. See Adair v. Sherman, 230 F.3d 890, 893 (7th Cir. 2000); Soverain Software LLC v. Victoria’s Secret Direct Brand Mgmt., LLC, 778 F.3d 1311, 1315 (Fed. Cir. 2015).
Here, the dispute centered on the first two elements—whether the patent infringement issues in WARF I and WARF II are identical. According to WARF, the literal infringement issue litigated in WARF I is materially different from the doctrine of equivalents issue to be litigated in WARF II. Decision at 21-22. In support, WARF relied on a single quotation from the Supreme Court’s decision in B&B Hardware, Inc. v. Hargis Indus., Inc., 575 U.S. 138, 154 (2015) for the notion that “[i]ssues are not identical if the second action involves application of a different legal standard, even though the factual setting of both suits may be the same.” Id. at 154. Despite the apparent relevance of that quoted language to WARF’s argument, the Federal Circuit found that the facts of B&B Hardware favored Apple.
In B&B Hardware, the Supreme Court considered whether a ruling by the Trademark Trial and Appeal Board (TTAB) could preclude relitigation of the same issue in a federal district court. Although the TTAB and district court proceedings arose from separate statutory frameworks with different objectives in mind—15 U.S.C. § 1052 (trademark registration) and 15 U.S.C. § 1114 (trademark infringement)—both statutes require application of the same likelihood-of-confusion test to the trademark at issue. At the TTAB, B&B opposed Hargis’s attempt to register a trademark, arguing that it was confusingly similar to B&B’s existing trademark. The TTAB ruled in favor of B&B, finding a likelihood of confusion. The Supreme Court held that the TTAB’s decision thereafter precluded Hargis from contesting likelihood of confusion as a defense in the parallel trademark infringement lawsuit initiated by B&B against Hargis in the district court. The Supreme Court explained that minor differences in how the same legal standard was applied did not prevent the preclusion of Hargis’s later trademark infringement defense by collateral estoppel. Specifically, the Supreme Court held that “minor variations in the application of what is in essence the same legal standard do not defeat preclusion.” Id.
Applying this reasoning, the Federal Circuit noted that both literal infringement and the doctrine of equivalents arise from the same statutory provision—35 U.S.C. § 271(a), which defines direct infringement. The court reasoned, therefore, that while literal infringement and the doctrine of equivalents involve different tests, they are both grounded in the same statute and ultimately address the same issue—whether the accused product directly infringes the patent. The Federal Circuit thus expressly articulated for the first time that literal infringement and the doctrine of equivalents are not separate issues for preclusion purposes—both address the same issue of direct infringement under § 271(a). Decision at 30-31 (citing Nystrom v. Trex Co., 580 F.3d 1281, 1286 (Fed. Cir. 2009) (second suit under doctrine of equivalents not permitted); Aspex Eyewear, Inc. v. Marchon Eyewear, Inc., 672 F.3d 1335, 1343 (Fed. Cir. 2012) (clarifying that Nystrom applied doctrine of issue preclusion)). The Federal Circuit reasoned that to hold otherwise would allow patent holders to litigate the same § 271(a) direct infringement claim twice, shifting from one theory to the other in the event of an unfavorable outcome. Decision at 31-32 (citing Galderma Labs., L.P. v. Amneal Pharms., LLC, 337 F. Supp. 3d. 371, 411 (D. Del. 2018) (not treating literal and doctrine-of-equivalents infringement as a single issue would result in “a decidedly wasteful use of judicial resources”)).
Finally, WARF argued that issue preclusion should not apply because the A9 and A10 processors are not the same products, i.e., not the A7 and A8 processors that were litigated in WARF I. The Federal Circuit rejected this argument, citing ArcelorMittal Atlantique et Lorraine v. AK Steel Corp., 908 F.3d 1267, 1274 (Fed. Cir. 2018), which held that issue preclusion can apply to different products if they are “essentially the same.” Ultimately, the court found no clear error in the district court’s determination that the LSD Predictors in the A7/A8 and A9/A10 processors are “essentially the same” for purposes of the asserted patent claims. Thus, the Federal Circuit’s prior judgment of no literal infringement in WARF I concerning the A7 and A8 processors applied with equal force to the A9 and A10 processors in WARF II. Decision at 26. This factual finding was echoed in the Federal Circuit’s application of the Kessler doctrine.
Issue 3: Application of the Kessler Doctrine
The Federal Circuit similarly determined that WARF’s infringement claims against the A9 and A10 processors in WARF II were barred by the Kessler doctrine, an often-overlooked legal principle established by the U.S. Supreme Court in Kessler, 206 U.S. at 285. Like issue preclusion, but for different reasons, this doctrine also prevents a patent holder from repeatedly asserting the same patent infringement claims against the same accused infringer once a court has ruled that the accused product does not infringe. Indeed, the doctrine was established to fulfill a purpose related to, but distinct from, claim preclusion. The Kessler doctrine is aimed, not at protecting the same accused infringer, but instead at protecting the same product from later infringement claims even if the patent owner accuses a different, unrelated party of infringement. The doctrine thus immunizes the product from subsequent infringement claims, regardless of who makes, uses, or sells it.
In this case, Apple invoked the Kessler doctrine to argue that the Federal Circuit’s ruling of non-infringement in WARF I immunized not only its A7 and A8 processors but also the A9 and A10 processors at issue in WARF II. As with issue preclusion, Apple maintained that the A9 and A10 processors were merely updated versions of the A7 and A8 processors and, therefore, should receive the same protection under the Kessler doctrine. WARF, however, countered that the Kessler doctrine does not apply because the A9 and A10 processors were not actually litigated in WARF I. And because the A9 and A10 processors are not the “same products” as the earlier adjudicated processors, they cannot benefit from the earlier non-infringement ruling. Decision at 35-36.
The Federal Circuit agreed with Apple and affirmed the district court’s conclusion that the Kessler doctrine barred WARF’s claims against the A9 and A10 processors. Noting that it had “applied the Kessler doctrine in limited circumstances,” the Federal Circuit nevertheless found that its precedent determined the outcome in this case. Decision at 33. For example, in Brain Life v. Elekta Inc., 746 F.3d 1045, 1056 (Fed. Cir. 2014), the court applied the Kessler doctrine to bar a second lawsuit asserting the patent’s method claims after the patent holder had unsuccessfully asserted the patent’s apparatus claims in an earlier lawsuit. The court explained that once the accused products were adjudged to be non-infringing with respect to the asserted apparatus claims, the defendant was “free to continue engaging in the accused commercial activity as a non-infringer.” Id. at 1058. This applied even though the second lawsuit involved allegations concerning later versions of the previously adjudicated products. The court concluded that because there were “no material differences” between the products in the two suits, the Kessler doctrine barred the second lawsuit. Id.
In SpeedTrack v. Office Depot, Inc., 791 F.3d 1317, 1329 (Fed. Cir. 2015), the plaintiff, SpeedTrack, moved to amend its infringement contentions to include the doctrine of equivalents shortly after Office Depot moved for summary judgment of no literal infringement. The district court denied SpeedTrack’s motion to amend and entered summary judgment of non-infringement in favor of Office Depot. In response, SpeedTrack filed a second lawsuit, this time asserting infringement under the doctrine of equivalents. The Federal Circuit affirmed the dismissal of the second suit under the Kessler doctrine. In doing so, the court explained that the Kessler doctrine plays a necessary gap-filling role, extending the protections afforded by claim and issue preclusion to avoid “the type of harassment the Supreme Court sought to prevent in Kessler.” Id. (quoting SpeedTrack, 791 F.3d at 1328).
Applying this precedent, the Federal Circuit found that WARF’s later-attempt to litigate the A9 and A10 processors under the doctrine of equivalents was barred by the Kessler doctrine for the reasons stated in Brain Life and SpeedTrack. The court emphasized that there was little difference between the facts in SpeedTrack and WARF, except that SpeedTrack involved the same product across both suits, whereas WARF accused subsequent versions of the previously adjudicated processors. However, as the court found in Brain Life, the non-infringing status of a product applies to subsequent versions of the product as long as there are “no material differences” between the products in each suit. Decision at 35. Because the court found the A9 and A10 processors to be essentially the same as the non-infringing A7 and A8 processors, the Kessler doctrine barred WARF’s second lawsuit. Id.
Finally, the Federal Circuit also rejected WARF’s argument that the Kessler doctrine did not apply because many of the A9 and A10 processors were sold before the final judgment of non-infringement in WARF I. The Federal Circuit clarified that the Kessler doctrine bars claims against products sold both before and after a final judgment of non-infringement, as suggested by the court’s holding in SpeedTrack. See SpeedTrack, 791 F.3d at 1318 (“the Kessler doctrine precludes SpeedTrack’s claims in full”). The court, therefore, concluded that WARF’s claims against Apple’s A9 and A10 processors were properly and completely barred under the Kessler doctrine. Decision at 36.
Conclusion
The Federal Circuit’s decision in WARF v. Apple not only clarified the principles of waiver and issue preclusion but also revitalized the often-overlooked Kessler doctrine as a potent tool ensuring finality in patent litigation. By confirming that literal infringement and the doctrine of equivalents are treated as the same issue for preclusion purposes, and by applying the Kessler doctrine to later generations of Apple’s processors, the court effectively ended WARF’s decade-long pursuit of enforcing the ’752 patent against Apple. For patent practitioners, these rulings underscore the need for patent holders to carefully consider the full scope and implications of their infringement theories, as procedural choices and strategic decisions made early in a case may limit future opportunities to relitigate similar claims.
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