New York: W.W.Norton & Company, 1988,
Buku Referensi
Sethi, S. Prakash
Prentice-Hall, 1974
Buku Teks
Douglas, William O.
Princeton University Press, 1960
Buku Teks
Douglas, William O.
Princeton University Press , 1960
Buku Teks SO
Sitkoff, Harvard
Oxford University Press, 2000
Buku Teks