Submitted on: 10 July 2003.
Revised on: 23 October 2003.
Accepted on: 25 November 2003.
___________________JOURNAL OF COMPLEXITY---ACADEMIC PRESS INC ELSEVIER SCIENCE
Submitted on: 23 July 1998.
Revised on: 30 September 1998.
Accepted on: 15 October 1998.
___________________JOURNAL OF COMPLEXITY---ACADEMIC PRESS INC ELSEVIER SCIENCE
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