Wichman, K., author
New York, David Mckay Company
Buku Referensi
Wely, F Prick van, author
London, Cassell
Buku Referensi
Berlin Hodder and Stoughton 1966
Buku Referensi
London, London Longmans
Buku Referensi
London; Cassell LTD., 1978
Buku Referensi