Wojciechowski, Jerzy A.
Council for research in values and philosophy, [Date of publication not identified]
Buku Teks SO
Morton, Adam
Blackwell, 1997
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O`Brien, Dan
Polity Press, 2006
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Wilson, Edward O.
Alfred A. Knoff, 1998
Buku Teks SO
Cowan, Henry J.
Van Nostrand Reinhold, 1981
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