請求項用語的修正

請求項用語中，單複數的問題必需小心，單複數的使用最好同一。

Superior’s patent claimed a safer, more efficient in-wall fireplace unit. Unfortunately for Superior, the patent issued with a mistake in its one independent claim, which referred to both "rear walls" (plural) and "the rear wall" (singular). According to Superior, it was unaware of this inconsistency in its patent until after it sued Majestic. When it learned of the mistake, Superior sought and received a certificate of correction from the Patent and Trademark Office (PTO), correcting "rear walls" to "rear wall."

Upon Majestic’s motion for summary judgment, the district court declared the certificate invalid. Affirming, the Federal Circuit held that a mistake in a claim, the correction of which broadens the scope of coverage of that claim and is not clearly evident from the specification, drawings and prosecution history, is not a "mistake of a clerical or typographical nature" subject to correction under § 255. The court also held that a mistake, the correction of which broadens a claim, is not a "mistake of . . . minor character" subject to correction under § 255. While the two claim limitations at issue were mutually inconsistent, it was not clear from the prosecution history which of the two variants was correct. Accordingly, a broadening certificate of correction should not have issued.