Dickerson, Reed
Little, Brown and Company, 1954
Buku Teks SO
Thornton, G.C.
Butterworth, 1987
Buku Teks SO
Bakshi, P.M.
N.M. Tripathi Private Limited, 1972
Buku Teks SO
International Monetary Fund, 1996
Buku Teks
International Monetary Fund, 1998
Buku Teks