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April 28, 2021 | By Mehdi D. Sheikerz
Posted in: S&H IP Blog | U.S. Court of Appeals For The Federal Circuit

“AT LEAST ONE …” – The Trend to Clarify Ambiguities

Claim definiteness is increasingly playing a more critical role in claim construction, considering the scrutiny afforded petitioners in inter-partes examination proceedings (IPRs) challenging validity of patents before the USPTO. Even though indefiniteness is not a basis to institute an IPR, claim indefiniteness can cause claim construction confusion.

The trend to clarify ambiguities and therefore avoid indefiniteness in claim language may have started before availability of IPRs as indicated by the Superguide Corp v. DirectTV Enterprises, Inc., 358 F.3d 870 (Fed. Cir. 2004) decision where the short claim expression “at least one” modifying a list of items caused considerable ambiguity in interpreting the claims of the patent.

In the Superguide decision, the court decided that “at least one” before a list of items modifies each item in the list, so that the claim requires each of the items in the list to be present for literal infringement. The court based its decision on the fact that the specification did not provide alternative examples where other combinations of the listed items may be contemplated.

Subsequent decisions by the U.S. Court of Appeals for the Federal Circuit seem to have also adopted the Superguide reasoning to some extent. In Enzo Biochem Inc. v. Applera Corp., 780 F.3d 1149 (Fed. Cir. 2015), the Federal Circuit reversed the District Court’s infringement decision when considering the claim expression “wherein A comprises at least three carbon atoms and represents at least one component of a signaling moiety capable of producing a detectable signal ….” The Federal Circuit’s reasoned that the meaning of the disputed claim expression in view of the specification requires that a signaling moiety be composed of components, of which at least one component is ‘A’ in combination with the other components and “not that ‘A’ itself can be a signaling moiety.

See also SIMO Holdings, Inc. v. Hong Kong uCloudlink Network Technology Limited (Fed. Cir. Jan. 5, 2021).

Therefore, it seems likely that “at least one” followed by a list of items may be interpreted to modify each item in the list as a conjunctive list to require all items in the list for finding infringement.

To help avoid an unintended interpretation, patent application drafters can consider explaining the intent of using “at least one” either by defining the expression or providing examples.


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