Keegan, Warren J., author
Alex Media Komputindo, 1992
Buku Teks
Johannsen, Hano, author
Crest Publishing House, 1999
Buku Referensi
Encyclopaedia Britannica Inc., 1967
Buku Referensi
Encyclopaedia Britannica Inc., 1968
Buku Referensi
Grolier Society of Australia, 1983
Buku Referensi