Gunn, Geoffrey C.
Boulder Westview Press 1990,
Buku Teks
Williams, E.N.
Penguin Books, 1970
Buku Teks
Daly, Frederick Michael
Melbourne Sun Books 1978
Buku Teks
State University of New York Press, 2001
Buku Teks
New Jersey Prentice-Hall 1965
Buku Teks