Eskridge, William N.
St. Paul Minn, 1988
Buku Teks
Ivamy, E.R. Hardy
Butterworth, 1995
Buku Teks
Gray, Oscar S.
The Bureau of National Affairs, 1973
Buku Teks
Snape, John
Blacks stone press limited, 1999
Buku Teks
Ginsburg, Jane C., author
Michie, 1996
Buku Teks