Walker, E. Ronald, author
University of Chicago Press, 1947
Buku Teks
North, Douglass C.
Harper & Row, 1971
Buku Teks
Zischka, Anton
Wilhelm Goldmann verlag , 1936
Buku Teks
Palvia, Chand Mal
Institute of Social Studies, 1953
Buku Teks
Schiller, Bradley R., author
Prentica-Hall , 1975
Buku Teks