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TAKEAWAY: When drafting or amending claims, carefully consider the plain and ordinary meaning of “at least one of A, B, and C,” which may be narrowly construed, as compared to that of “at least one of A, B, or C,” which may be more broadly construed.

When drafting and amending claims in a patent application, the use of the conjunctive “and” or the disjunctive “or” should be carefully considered, as each word of a claim can affect its interpretation and the ultimate validity of the patent. In particular, in claims reciting a selection from a list of elements that follows the phrase “at least one of,” one should consider how to encompass the claim scope intended.

The decisions of the U.S. Court of Appeals for the Federal Circuit in SuperGuide Corp. v. DirecTV Enterprises, Inc. (358 F.3d 870 (Fed. Cir. 2004)) and of the Patent Trial and Appeal Board (PTAB) of the U.S. Patent and Trademark Office (USPTO) in Ex parte Jung (Appeal No. 2016-008290 (PTAB March 22, 2017)) are frequently cited for guidance on the use of conjunctive and disjunctive claim language. In SuperGuide, the Federal Circuit found that the meaning of “at least one of A and B” is “at least one of A and at least one of B.” By contrast, the meaning of “at least one of A or B” would require A or B, but not both. This reasoning was followed by the PTAB regarding similar claim language in Ex parte Jung, wherein a new ground of rejection was cited against the appellant’s claims when the conjunctive “and” interpretation was found to lack written description support in the specification. Ex parte Jung was initially designated by the PTAB as informative but was subsequently de-designated to avoid confusion as to whether it reflected a change in the USPTO’s approach to claim construction.

The USPTO’s Manual of Patent Examining Procedure (MPEP) provides that a Markush group, typically employing the language “selected from the group consisting of,” may be used to recite a group of alternatives. To be proper, the group must be closed (i.e., not so expansive that persons skilled in the art cannot determine the metes and bounds of the claimed invention), and the members of the group must share a single structural similarity and a common use. MPEP §§ 2117, 2173.05(h). But, as the Federal Circuit noted in its recent decision in Amgen v. Amneal Pharm. LLC (Appeal Nos. 2018-2414, 2019-1086 (Fed. Cir. January 7, 2020)), although a Markush group itself may be closed by virtue of the phrase “consisting of,” the claim as a whole can still be open by virtue of the phrase “comprising,” in a claim’s preamble.

These guideposts should be kept in mind when drafting applications and claims. For example, in cases in which an applicant wishes to encompass the broadest scope, it may be helpful to employ Markush language, such as “at least one selected from the group of A, B, C, and combinations thereof,” to make sure to cover combinations and sub-combinations of the listed elements. Applicants should also give thought to narrower scope when it may be helpful to expressly omit certain combinations. The specification should provide support for all intended meanings, particularly in light of the potential for distinguishing over prior art during prosecution and/or when seeking rights abroad in jurisdictions that require literal written description support for claim amendments.