Weissenbruch , 1959
Buku Teks
Wolf, Charles, author
Syracuse University Press, 1958
Buku Teks
Prentice-Hall, 1949
Buku Teks
Fituni, L.A., author
Progress Publishers, 1963
Buku Teks
Nurkse, Ragnar, 1907-1959, author
Oxford University Press, 1961
Buku Teks