Wagner, RIchard E.
Little, Brown and Company, 1983
Buku Teks
Buchanan, James M., author
Liberty Fund, Inc., 1999
Buku Referensi
Appleby, Paul H., author
Louisiana State University Press, 1952
Buku Teks
Herring, E. Pendleton, author
McGraw-Hill, 1936
Buku Teks
Althaus, Scott L., author
Cambridge University Press, 2003
Buku Teks