James P Sterba
Routledge, 2001
Buku Teks
Pott, William S.A.
Alfred Kroner, 1925
Buku Teks
edited by Carl J. Friedrich
The Modern Library, 1949
Buku Teks
Gouch, J.W., author
Clarendon Press, 1950
Buku Teks
Tannenbaum, Donald G., author
Wadsworth/Thomson learning, 2004
Buku Teks