Where a document cited in the search report refers to a non-written disclosure, the letter "O'' is entered (see B‑VI, 2). Examples of such disclosures include conference proceedings. In cases where the oral disclosure took place at an officially recognised exhibition (Art. 55(1)(b)), see B‑VI, 5.5. The document category "O" is always accompanied by a symbol indicating the relevance of the document according to B‑X, 9.2.1, or B-X, 9.2.2, for example: "O, X"; "O, Y"; or "O, A".[Rule 61(4); ]