ABSTRACT
Technical Report 788, Department of Computer Science, Courant Institute of Mathematical Sciences, New York University, New York, September
The work of the first author was supported in part by the National Science
Foundation under Grants NSF-CCR-9732208. The work of the second author was supported in part by the National Science Foundation under Grants NSF-
CCR-9732208 and in part by the U.S. Department of Energy under Contract
DE-FG02-92ER25127.
