1. : Prolegomena to Library Classification, ASIA Publishing House, London 1967, p. 329 (Chapter MB).
2. : Vocabulary Control for Information Retrieval, Information Resources Press, Washington, DC 1972, especially p. 1, 139.
3. : Indexing Languages and Thesauri, Melville Publishing Company, Los Angeles, CA 1974.
4. : On Retrieval System Theory, Butterworths, London 1968, p. 65.