In the past, in the Universe of Documents, the general trend has been to narrow the extension of a subject embodied in -a document taken as a whole. Therefore, there has been a general tendency not to bring into one and the same document, compound subjects going with the different basic subjects, except in the case of complex subjects involving phase relation and the subjects involving the use of subject device in forming or sharpening isolate facets. In recent years„however, interdisciplinary team research has often, for practical convenience, necessitated bringing together in one and the same document two or more compound subjects going with different BS.