West, E.G., author
Airlington House, 1969
Buku Teks
Harris, Harry, author
Gadjah Mada University Press, 1980
Buku Teks
Buchanan, James M., author
Liberty Fund, 1999
Buku Referensi
Aviado, Domngo M.
The Williams & Wilkins Company, 1972
Buku Teks
Hougen, Olaf A., author
John Wiley & Sons, 1943
Buku Teks