Perthel, Dirk, author
Amsterdam University, 1981
Buku Teks
Hess, Peter
Harcourt Brace & Company, 1997
Buku Teks
Bryce, Murray D., author
McGraw-Hill, 1960
Buku Teks
Lockwood, William W., author
Princeton Princeton University Press , 1954
Buku Teks
Dam, Kenneth W., author
The Brooking Institution, 2006
Buku Teks