Bai v. L & L Wings, Inc., No. 98-1008, 1998 U.S. App. LEXIS 27994 (Fed. Cir. Nov. 3, 1998).


There is no infringement of patent when prosecution history estoppel precludes the plaintiff patentee's application of the doctrine of equivalents.



Carl B. Bai is the inventor and owner of U.S. Patent No. 4,017,076 (the '076 patent), directed to a target glove used in a game of catch. He asserted that Wings's MAGIC CATCH target game infringes claim 1 of his patent. Claim 1 of the '076 patent specifically mentions a "glove formed of a hemispherical dish-shaped rigid plastic member." The MAGIC CATCH glove is not hemispherical but rather saucer-shaped.

In prosecution, the examiner rejected claims 1-3 of Bai's application, stating that it would be an obvious combination of prior art patents to combine a dish-shaped structure with a target. In response, Bai canceled dependent claims 2 and 3 and amended claim 1 to add the limitation that the glove was "hemispherical." Bai remarked that he was amending claim 1 to "specifically and expressly recite the structural details" of his invention, noting its "particular configuration." Bai, at para 4. The examiner then allowed the amended claim 1.

On the question of infringement, the parties filed cross-motions for summary judgment focusing on the term "hemispherical." The district court construed the term "hemispherical" to include structures that are "less than a sphere, but . . . nevertheless, a part of a sphere." Bai v. L & L Wings, Inc., 1997 WL 527870 at *3. The district court held that the MAGIC CATCH's "perceptibly flattened surface" did not literally infringe claim 1 because it did not meet the "hemispherical" claim limitation. The district court also concluded that Bai added the term "hemispherical" in response to the 35 U.S.C. §103 obviousness rejection and that Bai did not establish that this amendment was unrelated to patentability.



1. Whether the trial court erred in granting Wings's motion for summary judgment by improperly concluding that Wings's MAGIC CATCH device does not read on Bai's claim 1 either literally or under the doctrine of equivalents.

2. Whether MAGIC CATCH literally infringed Bai's patent.


1. No. The district court correctly concluded that Bai added the term "hemispherical" to overcome prior art. Because prosecution history estoppel applies, no reasonable jury could find that the MAGIC CATCH device infringes every limitation recited in the properly construed claim 1 of the '076 patent under the doctrine of equivalents.

2. No. MAGIC CATCH was found to be predominantly flat with curved edges, not hemispherical like the '076 patent.


Cases Cited by the Court

Other Sources Cited by the Court

Involved Patents


State of the Law Before Bai

Warner-Jenkinson v. Hilton Davis

The Supreme Court in Warner-Jenkinson v. Hilton Davis Chem. Co., 520 U.S. 17, 117 S. Ct. 1040, 41 U.S.P.Q.2d 1865 (1997), the leading case on the doctrine of equivalents, made clear that summary judgment could in fact be applied to infringement claims under the doctrine. When a doctrine of equivalents claim is raised, summary judgment is proper when either (1) no reasonable jury could determine that the items in question are equivalent or (2) when prosecution history estoppel applies leaving no issue for the jury at all.

Regarding prosecution history estoppel, whether it applies under the doctrine of equivalents is a question of law that is reviewed de novo by the Federal Circuit. See Southwall Techs v. Cardinal IG Co., 54 F.3d 1570, 1579 (Fed. Cir. 1995).

Test Applied in Summary Judgment Determinations of Doctrine of Equivalents Claims

Based on the holding in Warner-Jenkinson, in determining whether summary judgment should be granted for doctrine of equivalents claims, a court first asks if prosecution history estoppel applies. See Wang Labs, Inc. v. Mitsubishi Elecs., 103 F.3d 1571, 1578 (Fed. Cir. 1997). If it does not, the court then asks whether the patented and accused devices have any equivalent elements. See Warner-Jenkinson. Under the doctrine of equivalents, an item that does not "literally infringe upon the express terms of a patent claim may nonetheless be found to infringe if there is 'equivalence' between the elements of the accused product or process and the claimed elements of the patented invention." Id. at 1043.

When Does Prosecution History Estoppel Apply

In ascertaining if prosecution history estoppel applies, the first question asked is why the applicant changed the language of the claims. See Warner-Jenkinson at 1050. If a patentee's amendments substantially change a claim to directly address an examiner's prior art rejection, prosecution history estoppel applies and surrendered subject matter cannot be asserted.

If there is no apparent reason for the amendment to the claim, Warner-Jenkinson teaches that the court is to presume that the change was made for patentability purposes. Such a presumption can be rebutted by the patentee establishing that the change was not, in fact, related to patentability. If the patentee is successful in its efforts to persuade the court of this, a grant of summary judgment for the alleged infringer would be improper.

When Does Prosecution History Estoppel Not Apply

If, on the other hand, the court determines as a matter of law that prosecution history estoppel does not apply, Warner-Jenkinson held that the court must determine whether a reasonable jury could find that any element of the two devices has any equivalent attribute.

Effect of Bai on Current Law

The court held that in the absence of a reason for amending a claim after a rejection by the examiner, the Warner-Jenkinson presumption dictates that the court treat the amendment as related to patentability. In other words, the court will interpret an absence of justification for amending a claim as the patent applicant trying to overcome the rejection. The implication for practitioners is to always, where possible, state reasons unrelated to patentability for amending a claim. Failure to adequately justify the change will result in a court assuming that the amendment was intended to cure patentability defects highlighted by the examiner.

The Federal Circuit in Bai, however, held that the Warner-Jenkinson presumption does not apply to the '076 patent. The court states that the prosecution record makes clear that the amendment was for patentability purposes. It rejects the argument that the applicant was clarifying its original claims because there is no evidence which indicates that clarity was a problem. Moreover, the court took applicant's assertion that it was reciting a particular configuration as evidence that it was a narrowing amendment necessary to distinguish the invention from prior art in response to the examiner's rejection. The court concluded that when an applicant fails to prevail over an examiner's rejection by argument, "he has two choices: either to amend the claim or to appeal the rejection." Bai at para. 20. The implication is that to ensure that a court does not infer that the amendment addresses a prior art rejection, the applicant should appeal the rejection. Only then, should the applicant attempt to amend the claim.

Practitioners should note that a court is likely to require more than a token justification for an amendment. The Federal Circuit stated that "Bai's boilerplate remark to the examiner that he amended his claims to 'specifically and expressly recite the structural details' of his invention does not affect our conclusion." Bai at para. 18. In the face of applicant's failure to prevail by argument over examiner's rejection, the court will presume that an amendment is related to patentability.

Unanswered Questions

It is for the judge to decide whether, as a matter of law, prosecution history estoppel or the Warner-Jenkinson presumption apply. It is unclear once the Judge decides as a matter of law that prosecution history estoppel does not apply, but that the Warner-Jenkinson presumption does apply, who decides whether this presumption has been rebutted.

The court is also unclear about what language, when accompanying an amendment, would be sufficient to rebut the Warner-Jenkinson presumption. There is also no indication under what circumstances, if any, it would be appropriate to use an interference proceeding to rebut the Warner-Jenkinson presumption.

In addition, there is no guidance as to whether an applicant could avoid the Warner-Jenkinson presumption by separating dissimilar types of changes made to a claim, making all changes responsive to the examiner's rejections in one amendment and addressing other types of changes (for instance, textural clarifications) in a separate amendment.

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