Schwartz, Robert J., author
Crowell , 1955
Buku Referensi
Oxford University Press, 1996
Buku Referensi
Paxton, John, author
J.M. Dent & Sons, 1992
Buku Referensi
Jones, David J.
Second Back Row Press, 1981
Buku Teks
Jones, David J., author
Australia, Second Back Row Press
Buku Referensi