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
Tabb, William Murray
The Michie Company, 1992
Buku Teks
edited by D. J. Gijlstra and D. F. Murphy
Kluwer, 1984
Buku Teks