World Intellectual Property Organization. (1979). Official catchword index to the third edition (1979) of the International Patent Classification. C. Heymans Verlag KG.

World Intellectual Property Organization. Official Catchword Index to the Third Edition (1979) of the International Patent Classification. München: C. Heymans Verlag KG, 1979.

World Intellectual Property Organization. Official Catchword Index to the Third Edition (1979) of the International Patent Classification. C. Heymans Verlag KG, 1979.