egemen@cs.umd.edu, partially supported by NASA grant NAG 52895.

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beigel@cs.umd.edu, partially supported by NSF grants CCR-8958528 and CCR-9415410, and by NASA grant NAG 52895, on sabbatical from Yale University until 8/1/97.

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ben@cs.umd.edu, partially supported by NSF grants EEC-9402384 and IRI-9615534, and by NASA grant NAG 52895, also affiliated with the Institute for Systems Research.

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HCIL address: Department of Computer Science, U. of Maryland at College Park, College Park, MD 20742, USA, for more information: http://www.cs.umd.edu/projects/hcil.

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