Nicholson, Michael, author
Cambridge University Press, 1989
Buku Teks
Dunning, John H.
George Allen and Unwin , 1974
Buku Teks
Frrederick A. Praeger, 1960
Buku Teks
Westview Press, 1994
Buku Teks
Whyte, William Foote, author
Richard D. Irwin, 1959
Buku Teks