Rule 43(1)(a) and (b) define the two-part form which a claim should have "wherever appropriate". The first part should contain a statement indicating "the designation of the subject-matter of the invention" i.e. the general technical class of apparatus, process, etc. to which the invention relates, followed by a statement of "those technical features which are necessary for the definition of the claimed subject-matter but which, in combination, are part of the prior art". This statement of prior-art features is applicable only to independent claims and not to dependent claims (see III, 3.4). It is clear from the wording of Rule 43 that it is necessary only to refer to those prior- art features which are relevant to the invention. For example, if the invention relates to a photographic camera but the inventive step relates entirely to the shutter, it would be sufficient for the first part of the claim to read: "A photographic camera including a focal plane shutter" and there is no need to refer also to the other known features of a camera such as the lens and view-finder. The second part or "characterising portion" should state the features which the invention adds to the prior art, i.e. the technical features for which, in combination with the features stated in sub-paragraph (a) (the first part), protection is sought.

If a single document in the state of the art according to Art. 54(2), e.g. cited in the search report, reveals that one or more features in the second part of the claim were already known in combination with all the features in the first part of the claim and in that combination have the same effect as they have in the full combination according to the invention, the examiner should require that such feature or features be transferred to the first part. Where, however, a claim relates to a novel combination, and where the division of the features of the claim between the prior-art part and the characterising part could be made in more than one way without inaccuracy, the applicant should not be pressed, unless there are very substantial reasons, to adopt a different division of the features from that which he has chosen, if his version is not incorrect.