In July, the U.S. Patent & Trademark Office's Patent Trial and Appeal Board designated its ex parte Jung decision as informative (see here and here). In this decision, the Board held that the phrase "at least one of A and B" was presumed to be conjunctive. That is, the phrase was presumed to mean "at least one of A and at least one of B."
This holding raised some concern among patent practitioners, since the phrase "at least one of A and B" often is intended as shorthand for the Markush phrase "at least one selected from the group consisting of A and B." The construction of the phrase "at least one of A and B" as requiring at least one of A and at least one of B is significantly narrower than the Markush phrase of "at least one selected from the group consisting of A and B." The former only allows for the conjunctive embodiment in which both A and B are present. In contrast, the latter allows for additional, disjunctive embodiments, in which (i) A is present but B is absent, and (ii) B is present but A is absent.
In view of this narrow construction of "at least one of A and B" by the Board, the designation of ex parte Jung as informative in July raised additional concern among patent practitioners. Would this designation mean that the phrase "at least one of A and B" was presumed to be conjunctive during prosecution of any application whose claims recited the phrase?
Apparently in response to such concern, on August 7, 2018, the Board removed the informative designation from ex parte Jung. In its announcement, the Board stated:
It has come to PTAB's attention that the decision has not been read as intended. For example, the designation was not intended to reflect new or changed policies with respect to claim construction. As a result, in order to avoid any confusion, the decision has been de-designated and removed from the list of informative decisions. The case remains a routine decision of the Board.
Despite this de-designation of ex parte Jung as an informative decision, it may be beneficial to avoid the potentially ambiguous phrase of "at least one of A and B." This is especially the case if disjunctive embodiments are intended to be included within the scope of a claim. Alternative, unambiguous phrasing, such as "at least one selected from the group consisting of A and B," may be preferable to avoid a narrow, conjunctive, construction.
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