Green, William B.
Van Nostrand Reinhold Co., 1983
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Kleitz, William
Pearson/Prentice Hall, , 2008.
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Kleitz, William, author
Upper Saddle River, N.J. Prentice Hall 1996,
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Artikel Jurnal
Pratt, William K., author
John Wiley & Sons, 1978
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