Posner, Richard A.
The University of Chicago, 1976
Buku Teks
Calvani, Terry
Little, Brown, 1988
Buku Teks
edited by Werner Sichel
Ann Arbor, 1970
Buku Teks
Denoon, David B.H.
Council on Foreign Relations Press , 1993
Buku Teks
Hylton, Keith N, Author
Cambridge University Press, 2003
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