Simon, Herbert A., author
Alfred A. Knopf, 1973
Buku Teks
Denhardt, Robert B., author
Harcourt College, 1999
Buku Teks
Bartholomew, Paul C., author
Littlefield, Adams, 1959
Buku Teks
Herring, E. Pendleton, author
McGraw-Hill, 1936
Buku Teks
Denhardt, Robert B., author
Thomson, 2009
Buku Teks