Weatherill, Stephen
Blackstone Press Ltd., 1998
Buku Teks
Richard Crawford Pugh
St.paul Minn, 1993
Buku Teks
Jaffe, Louis L., author
Little, Brown, 1968
Buku Teks
Barrett, Edward L., author
Foundation Press, 1977
Buku Teks
Foote, Caleb, author
Little, Brown, 1980
Buku Teks