According to Rule 33.1(a) PCT and Rule 33.1(b) PCT, oral disclosure, use, exhibition, etc. are recognised as prior art only when this is substantiated by a written disclosure. In contrast, according to Art. 54 EPC, a public oral description, use, etc. is considered as prior art. However, the examiner, in carrying out a European search, should cite an oral description, etc. as prior art only if he has available a written confirmation or is otherwise convinced that the facts can be proved. Such references to oral disclosure, prior public use, disclosure by sale, etc. are more usually brought up by opponents in opposition proceedings (see G‑IV, 7.1 to G-IV, 7.4).