Artikel Jurnal
Johansson, Per-Olov, author
Cambridge Univ. Press , 1987
Buku Teks
Irina Farquhar, Kent Summers, Alan Sorkin, editor
JAI, 2001
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Fogel, Robert William, author
Johns Hopkins Press, 1964
Buku Teks
Peterson, Wallace C.
W.W. Norton & Co., 1962
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