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Submitted on: 15 June 2006.
Revised on: 26 July 2006.
Accepted on: 31 August 2006.
___________________JOURNAL OF LOGIC AND COMPUTATION
Submitted on: 30 September 2005.
Revised on: 10 November 2005.
Accepted on: 28 November 2005.
___________________JOURNAL OF LOGIC AND COMPUTATION
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Submitted on: 24 November 2011.
Revised on: 29 February 2012.
Accepted on: 06 April 2012.
___________________JOURNAL OF LOGIC AND COMPUTATION
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