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Submitted on: 02 November 2001.
Revised on: 26 January 2002.
Accepted on: 26 March 2002.
___________________JOURNAL OF THE ACM---ASSOC COMPUTING MACHINERY
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Submitted on: 27 September 2001.
Revised on: 20 January 2002.
Accepted on: 21 February 2002.
___________________JOURNAL OF THE ACM---ASSOC COMPUTING MACHINERY
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Submitted on: 11 February 1999.
Revised on: 15 April 1999.
Accepted on: 07 June 1999.
___________________JOURNAL OF THE ACM---ASSOC COMPUTING MACHINERY
Submitted on: 06 June 1998.
Revised on: 19 September 1998.
Accepted on: 24 October 1998.
___________________JOURNAL OF THE ACM---ASSOC COMPUTING MACHINERY
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