Carter, Gwendolen M.
Frederick A. Praeger, 1961
Buku Teks SO
Mires, Charlene
University of Pennsylvania Press, 2002
Buku Teks
Mass., A. J. St. Onge, 1970
Buku Teks SO
by Albert P. Blaustein, Jay Sigler, Benjamin R. Beede, with Wayne E. Olson
Oceana Publications, 1977
Buku Referensi
Furnivall, JS
Solidaridad publishing house, 1974
Buku Teks