Schwab, Glenn Orville, 1919-
New York: John Wiley & Sons, 1957
Buku Teks
Broek, David
Martinus Nijhoff, 1982
Buku Teks SO
Peters, Max
McGraw-Hill, 1984
Buku Teks SO
Clayton, Albert E.
Longmans, 1966
Buku Teks
Ullmann, Manfred
Edinburgh University Press, 1978
Buku Teks SO