E.Zaleski
Organisation for Economic Cooperation and Development, 1969
Buku Teks
Holzman, Franklyn D.
Harvard University Press, 1962
Buku Teks
Hodgman, Donald R.
Harvard University Press, 1954
Buku Teks
Feiwel, George R.
Praeger Pub., 1972
Buku Teks
Bergson, Abram
Harvard University Press , 1961
Buku Teks