Harkins, William E., author
Littlefield, Adams, 1959
Buku Referensi
Watt, Homer A., author
Barnes & Noble, 1957
Buku Referensi
edited by Joseph T. Shipley
Littlefield, Adams, 1960
Buku Referensi
Oxford University Press, 1996
Buku Referensi
Katzner, Kenneth, author
John Wiley & Sons, 1994
Buku Referensi