In deciding how specific the essential features must be, the provisions of Art. 83 should be borne in mind: it is sufficient if the application as a whole describes the necessary characteristics of an invention in a degree of detail such that a person skilled in the art can perform the invention (see F-III, 3). It is not necessary to include all details of the invention in the independent claim. Thus a certain degree of generalisation of the claimed features may be permitted, provided that the claimed generalised features as a whole allow the problem to be solved. In this case a more specific definition of the features is not required. This principle applies equally to structural and functional features.