Kempin, Frederick G
West Publishing Co, 1973
Buku Teks
Angle, Paul M.
Rand McNally , 1958
Buku Teks
Rodgers, William H., author
St. Paul Minn, 1977
Buku Teks
Schwartz, Bernard, author
Little, Brown & Co., 1991
Buku Teks
Rodgers, William H., author
West Publishing, 1994
Buku Teks