Joppke, Christian, author
Polity Press, 2009
Buku Teks
Corcoran, A. C.
J.B. Lippincott, 1961
Buku Teks
Bouman, P. J. (Pieter Jan)
McGraw-Hill , 1954
Buku Teks
Frederick A, Praeger; George Allen and Unwin Ltd., 1964
Buku Teks
Thubron, Colin
Little, Brown and Company, 1967
Buku Teks