Elliot, Diane L
Philadelphia Lippincott - Raven 1997,
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Golden, Sidney
"Massachusetts: Addison-Wesley, 1961",
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Wallwork, S.C.
"London: Longmans, 1960",
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Nelson, Harry, author
New York West 1988,
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Strahler, Alan A., author
John Wiley & Sons, 1996
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