Tabb, William Murray
Michie, 1992
Buku Teks
Gray, Oscar S.
The Bureau of National Affairs, 1973
Buku Teks
Craig, Robin Kundis
Thomson/West, 2008
Buku Teks
Rose, Jerome G.
The State University of New Jersey, 1974
Buku Teks
Schlesinger, Rudolf B.
The Foundation Press, 1950
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