In T 136/95 (OJ 1998, 198), the board stated that identity of invention has to be assessed by reference to the skilled person. A patent application is a technical document, addressed to the skilled person, not a work intended for the general reader. However, the skilled person is not familiar, unlike in the assessment of inventive step, with all the prior art, but only with those elements of it which form part of his general knowledge, and it is on the basis of this knowledge, or by carrying out simple operations derived from it, that he may infer whether or not there is identity of invention. According to the board, it was necessary to give some flexibility to the requirement for identity of invention between the two applications. Some features claimed in the European application need not be expressly mentioned in the previous application whose priority is claimed, provided that the skilled person is able, purely on the basis of his knowledge or by performing simple operations to carry out the invention, to infer these features from the prior application. In the case in question a structural feature claimed in the European patent application was supported by a general functional feature described in the prior application.
In T 744/99 the board noted that for the subject-matter of a claim to be derivable "directly and unambiguously, using common general knowledge from the previous application as a whole" in accordance with G 2/98 (OJ 2001, 413), such subject-matter could not be novel with respect to the disclosure of the priority document. The application of common general knowledge could only serve to interpret the meaning of a technical disclosure and place it in context; it could not be used to complete an otherwise incomplete technical disclosure. Thus the board concluded in the case in hand that, since the priority document only disclosed a new signal protocol without any disclosure of a suitable receiver, claim 8 of the subsequent application, which was directed to such a receiver, was not entitled to the claimed priority date, but only to the filing date.
In case T 1312/08 the respondent (patent proprietor) had submitted that the definition of "PU" was correct in the patent in suit but erroneous in the priority document. In rejecting the respondent's arguments, the board referred to the established jurisprudence of the boards of appeal, and stated that the reworking of an example and especially of a method which was not a standardised one and was not reported in encyclopaedias, textbooks, dictionaries and handbooks could not be considered to be the application of common general knowledge. As a consequence, the mere fact that it was necessary to carry out a test, which was not part of common general knowledge, in order to find out whether the definition of PU in the priority document was erroneous made it clear that the different definition of PU used in the patent in suit was not derivable directly and unambiguously, using common general knowledge, from the whole content of the priority document. See also decision T 1579/08.