Hoag, John D.
George Braziller, 1963
Buku Teks SO
Jordan, R. Furneaux
Thames, [Date of publication not identified]
Buku Teks SO
Risebero, Bill
MIT Press, 2001
Buku Teks SO
Johnson, Elmer D.
Scarecrow Press, 1970
Buku Teks
editor in chief, Mortimer J. Adler
Encyclopedia Britanica, 1990
Buku Referensi