Haas, Ernst B.
Standford University Press, 1970
Buku Teks
Jenks, C. Wilfred
Stevens & Sons Limited, 1960
Buku Teks SO
edited by Willem A. Veenhoven
Martinus Nijhoff, 1976
Buku Teks SO
Gormley, W. Paul
A.W. Sijthoff, 1976
Buku Teks
Gibson, John S.
Praeger, 1991
Buku Teks SO