Martin, William J.
Brookfield, Vt., USA : Gower,, 1995.
Buku Teks
Currie, Wendy
John Wiley & Sons, 2000
Buku Teks
Barber, William J.
Stanford University, 1961
Buku Teks
Voich, Dan
South-Western Publishing Co, 1975
Buku Teks
Ahn, Mark J.
Probus Pub. Co, 1991
Buku Teks