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Copyright 2005 American Mathematical Society
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Brent Everitt
Department of Mathematics, University of York, York YO10 5DD, England
E-mail address: bje1@york.ac.uk
John Ratcliffe
Department of Mathematics, Vanderbilt University, Nashville, TN 37240
E-mail address: ratclifj@math.vanderbilt.edu
Steven Tschantz
Department of Mathematics, Vanderbilt University, Nashville, TN 37240
E-mail address: tschantz@math.vanderbilt.edu
The first author is grateful to the Mathematics Department, Vanderbilt University for its hospitality during a stay when the results of this paper were obtained.