Laski, Harold J., author
George Allen and Unwin, 1949
Buku Teks
Patterson, Thomas E., author
McGraw-Hill, 203
Buku Teks
William, Robin M.
Alfred, 1966
Buku Teks
Williams, Robin M., author
Alfred A. Knopf, 1961
Buku Teks
Williams, Robin W., author
Alfred A. Knopf, 1963
Buku Teks