Buku Referensi
Silverstein, Adam J.
Cambridge University Press, 2007
Buku Teks
Bettany, G.T., author
Bracken Books, [date of publication not identified]
Buku Referensi
editor in chief, Mortimer J. Adler
Encyclopedia Britanica, 1990
Buku Referensi
editor in cheief, Mortimer J. Adler
Encyclopedia Britanica, 1996
Buku Referensi