The third category is irrelevant matter. It should be noted, however, that such matter is specifically prohibited under Rule 48(1)(c) only if it is "obviously irrelevant or unnecessary", for instance, if it has no bearing on the subject-matter of the invention or its background of relevant prior art (see also F-II, 4.4). The matter to be removed may already be obviously irrelevant or unnecessary in the original description. It may, however, be matter which has become obviously irrelevant or unnecessary only in the course of the examination proceedings, e.g. owing to a limitation of the claims of the patent to one of originally several alternatives. When matter is removed from the description, it must not be incorporated into the patent specification by reference to the corresponding matter in the published application or in any other document (see also F-III, 8).