Seth, M.L.
S. Chand, 1969
Buku Teks
Krugman, Paul R.
Addison-Wesley , 1997
Buku Teks
Watson, Donald Stevenson
Houghton Miffiln, 1960
Buku Teks
Boulding, Kenneth Ewart, 1910-1993
Prentice-Hall, 1958
Buku Teks
edited by J.P. Nieuwenhuysen and P.J. Drake
Melbourne Unversity Press, 1977
Buku Teks