Hechscher, Gunnar, author
University of Minnesota Press, 1984
Buku Teks
Innes, Hammond, 1913-, author
Time Inc., 1963
Buku Teks
Boumol, William J.
Harvard University Press, 1952
Buku Teks
Heckscher, Gunnar
Buku Teks
Gough, Ian, author
Macmillan, 1992
Buku Teks