(1) Institute of Operations Research, University of Zürich, CH-8044 Zürich, Switzerland, klatte@ior.unizh.ch, CH;(2) Department of Mathematics and Statistics, Old Dominion University, Norfolk, Virginia 23529, wuli@math.odu.edu, US
Abstract:
Received October 26, 1996 / Revised version received October 1, 1997 Published online October 9, 1998