Spooner, F.P.
Fredereck A.Praeger Publisher, 1960
Buku Teks
edited by Patrick Giddy
The Council For Research In Values And Philosophy, 2001
Buku Teks
Lipton, Merle, author
Witwatersrand University Press, 1993
Buku Teks
Maasdorp, A.F.S., Sir
Juta & Co., 1948
Buku Teks
United Nations , 1990
Buku Teks