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In the case of Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., et al., petitioner Festo Corporation owns two patents for an industrial device. When the patent examiner rejected the initial application for the first patent because of defects in description [35 U. S. C. [section] 112], the application was amended to add the new limitations that the device would contain a pair of one-way sealing rings and that its outer sleeve would be made of a magnetizable material. The second patent also was amended during a reexamination proceeding to add the sealing rings limitation. After Festo began selling its device, respondents (SMC) entered the market with a similar device that uses one two-way sealing ring and a nonmagnetizable sleeve.
Festo filed suit, claiming that SMC's device is so similar that it infringes Festo's patents under the doctrine of equivalents. The district court ruled for Festo, rejecting SMC's argument that the prosecution history estopped Festo from saying that SMC's device is equivalent. A Federal Circuit panel initially affirmed, but the Supreme Court granted certiorari, vacated, and remanded in light of Warner-Jenkinson Co. v. Hilton Davis Chemical Co. [520 U.S. 17, 29], which had acknowledged that competitors may rely on the prosecution history to estop the patentee from recapturing subject matter surrendered by amendment as a condition of obtaining the patent.
On remand, the en banc Federal Circuit reversed, holding that prosecution history estoppel applied. The court ruled that estoppel …