Robert Maynard Hutchins, editor in chief
Encyclopaedia Britannica, Inc., 1952
Buku Referensi
Columbia University Press, 1991
Buku Teks
Artikel Jurnal
Ritter, Peck, author
Brooks/Cole Publishing, 1996
Buku Teks
Patten, Bradley M., author
McGraw-Hill, 1958
Buku Teks