Hough, Jerry F.
The Brookings Institution, 1980
Buku Teks
Lamont, Corliss, author
Philosophical Library, 1952
Buku Teks
Oxford University Press, 1951
Buku Teks
Dallin, David
Hollis & Carter, 1949
Buku Teks
Fischer, George, author
Harvard University Press, 1952
Buku Teks