Friedmann, Julian, author
Intellect, 2000
Buku Teks
Simpson, Thomas D., author
Prentice-Hall, 1987
Buku Teks
Hart, Albert Gailord, 1909-, author
Prentice-Hall, 1953
Buku Teks
Whittlesey, Charles R., author
Macmillan, 1954
Buku Teks
Culbertson, John M.
McGraw-Hill, 1972
Buku Teks