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Submitted on: 17 December 1999.
Revised on: 19 February 2000.
Accepted on: 19 March 2000.
___________________International Journal of Mathematical Engineering and Management Sciences
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Submitted on: 15 March 2000.
Revised on: 18 June 2000.
Accepted on: 11 July 2000.
___________________International Journal of Mathematical Engineering and Management Sciences