Stutely, Richard
Century Business, 1992
Buku Teks
Carnes, W. Stansbury, author
HarperBusiness, 1992
Buku Referensi
Perthel, Dirk, author
Amsterdam University, 1981
Buku Teks
Doody, Francis S.
New York, N.Y. Random c.1965,
Buku Teks
Unesco Press, 1979
Buku Teks