Schlesinger, Rudolf B.
The Foundation Press, 1950
Buku Teks
Kauper, Paul G.
Little, Brown, 1971
Buku Teks
Dine, Janet
Blackstone Press, 1993
Buku Teks
Weatherill, Stephen
Blackstone Press Ltd., 1998
Buku Teks
Pugh, Richard Crawford
St.paul Minn, 1993
Buku Teks