Patent professionals know that even seemingly straightforward words and phrases can become battlegrounds for outcome-determinative arguments. In patent law, where every word in a claim matters, courts and administrative bodies must often dissect common phrases that, in everyday life, we interpret effortlessly using context. One such phrase that has led to significant legal debate is "at least one of A and B."
At first glance, the phrase "at least one of A and B" might appear to have a clear meaning. However, its interpretation can shift dramatically depending on context, including whether A and B are understood as individual elements or as categories of elements. This seemingly minor distinction has been enough to sway decisions at both the Federal Circuit and the Patent Trial and Appeal Board (PTAB).
The Federal Circuit addressed this issue in SuperGuide Corp. v. DirecTV Enterprises, Inc., 358 F.3d 870 (Fed. Cir. 2004). In Superguide, the court had to determine the meaning of the phrase "at least one of a desired program start time, a desired program end time, and a desired program service." The court distinguished between whether the listed elements were categories or individual items:
If the elements are categories, the phrase is interpreted as "and," requiring that all listed elements be present. If the elements are individual items, the phrase is interpreted as "or,"meaning that satisfying any one of the elements suffices. This distinction is razor-thin but has profound implications for claim scope and enforceability.
The ambiguity in this phrase was highlighted again in Ex parte Jung, a PTAB decision that initially received the designation of an "informative" decision—signaling its importance—only for the PTAB to later withdraw that designation. The inconsistency underscores how challenging it can be to apply Superguide in practice.
Recently, Microsoft found itself impacted by this ambiguity in a PTAB decision. Appeal 2024-001081. Application 16/284,325. The claim on appeal is reproduced below:
A system comprising:
a memory; and
one or more processors coupled to the memory, the one or more processors configured to:
assign an optimization designation to each of a plurality of respective unoptimized regions of a file based at least in part on an amount of system resources utilized to access each respective region, where an amount of system resources utilized to access a first region is different from an amount of system resources utilized to access a second region and the first region is assigned a first optimization designation different from a second optimization designation assigned to the second region, each optimization designation indicating at least one of the following:
(a) a specified compression technique, which is selected from a plurality of compression
techniques, and
(b) a specified data de-duplication technique, which is selected from a plurality of data de-duplication techniques; and optimize each unoptimized region of the file based on the respective optimization designation assigned to the region.
Microsoft had argued for the "or" interpretation of "at least one of A and B," contending that the elements in question were specific items and citing the specification which allegedly included examples that supported the “or” interpretation. However, the PTAB disagreed and applied the "and" interpretation, meaning that the claim required both A and B. While this interpretation allowed Microsoft's claim to distinguish over the prior art, it was a Pyrrhic victory—the claims were unintentionally limited in a way that Microsoft had not intended.
From the decision:
...First, even if the Specification did disclose some embodiments with both items (e.g., both compression and deduplication) and other embodiments with just one (e.g., either compression or deduplication), “[i]t is not necessary that each claim read onevery embodiment.” Baran v. Med. Device Techs., Inc., 616 F.3d 1309, 1316 (Fed. Cir. 2010). An applicant is free to write a claim covering only one embodiment, not all embodiments. Second, the only cited paragraph does not support Appellant’s assertion that the Specification discloses embodiments of an optimization designation that indicates only a compression technique or only a duplication technique…
Thus, consistent with SuperGuide, we interpret “and” to mean “and,” and claim 8 therefore requires that each optimization designation indicate (a) at least one “specified compression technique” and (b) at least one “specified data de-duplication technique.” If Appellant wants the claim to instead permit alternatives, then Appellant may wish to amend “and” to “or” (e.g., “at least one of A or B”; “at least one A or at least one B”; or even simpler “A or B”). See, e.g., Schumer v. Lab. Computer Sys., Inc., 308 F.3d 1304, 1311 (Fed. Cir. 2002) (“We have consistently interpreted the word ‘or’ to mean that the items in the sequence are alternatives to each other.”).
The saga of "at least one of A and B" provides a cautionary tale for patent practitioners. Here are some potential tips to reduce unintended interpretations:
Clarify Intent Explicitly in the Specification – If the phrase "at least one of A and B" is used, consider defining explicitly whether "A and B" refers to categories or individual elements in the specification.
Use Alternative Wording – Instead of relying on "at least one of A and B," consider phrasing such as "at least one of A or at least one of B" (if an "or" interpretation is desired) or "at least one of each of A and B" (if an "and" interpretation is desired).
Anticipate Examiner and PTAB Scrutiny – Given the PTAB's history of inconsistency on this issue, be prepared to defend the chosen interpretation during prosecution.
Patent law is replete with examples of minor linguistic choices having significant legal consequences. The phrase "at least one of A and B" is a prime example of how splitting linguistic hairs can have major ramifications. As Superguide and subsequent PTAB decisions illustrate, even seasoned practitioners can find themselves caught in unintended claim scope traps. Careful drafting and proactive clarification can help ensure that claims mean precisely what their drafters intend.