Gilson, Christopher C.
Aspen Systems Corporation, 1979
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Ayres, James J., author
New York: John Wiley & Sons, 1990,
Buku Referensi
McKim, Amee R, author
Thomson West, 2009
Buku Teks
Reinhardt, George C.
Dobleday, 1960
Buku Teks
Myerson, Jeremy, author
Gingko Press, 1999
Buku Teks SO