Administrative Instructions under the Patent Cooperation Treaty
Indication of Citations of Particular Relevance in the International Search Report
(a) Where any document cited in the international search report is of particular relevance, the special indication required by Rule 43.5(c) shall consist of the letter(s) "X" and/or "Y" placed next to the citation of the said document.
(b) Category "X" is applicable where a document is such that when taken alone, a claimed invention cannot be considered novel or cannot be considered to involve an inventive step.
(c) Category "Y" is applicable where a document is such that a claimed invention cannot be considered to involve an inventive step when the document is combined with one or more other such documents, such combination being obvious to a person skilled in the art.