Submitted on: 28 September 2011.
Revised on: 14 November 2011.
Accepted on: 30 November 2011.
___________________ACM Transactions on Computation Theory
Submitted on: 14 July 2006.
Revised on: 08 August 2006.
Accepted on: 30 September 2006.
___________________ACM Transactions on Computation Theory
Submitted on: 24 January 1999.
Revised on: 23 April 1999.
Accepted on: 07 May 1999.
___________________ACM Transactions on Computation Theory
Submitted on: 28 December 2007.
Revised on: 12 April 2008.
Accepted on: 29 May 2008.
___________________ACM Transactions on Computation Theory
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