Bernhardt, Roger, author
West Publishing, 1993
Buku Teks
Cunningham, Roger A., author
West Pub., 1993
Buku Teks
Smith, Roger J., author
Longman, 2000
Buku Teks
Lawson, F.H., author
Clarendon Press, 1958
Buku Teks
Boyer, Ralph E., author
St. Paul Minn, 1991
Buku Teks