1992
Buku Teks
Mudie, Robyn
The University of Hull , 1998
Buku Teks
Rollason, Russell G., author
Alternative Pub. Cooperative, 1981
Buku Teks
Soemitro Djojohadikusumo, author
[publisher not identified], 1975
Buku Teks
Chicago : encyclopaedia Britanica Inc, 2000,
Buku Referensi