NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This project has been supported by the National Aeronautics and Space Administration under Grant No. NAG 5-6839, the Department of Energy under Contract No. DE-FG02-98ER-41069, and the National Science Foundation under Grant No. PHY-972-4780. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the sponsors.

Front cover: An example of a form of abstract composition known as Marian vectors, based on mathematical processes. Courtesy of the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

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