Submitted on: 18 October 2007.
Revised on: 05 December 2007.
Accepted on: 17 January 2008.
___________________Armenian Journal of Mathematics
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Submitted on: 12 February 2000.
Revised on: 08 March 2000.
Accepted on: 25 March 2000.
___________________Armenian Journal of Mathematics
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Submitted on: 16 September 2005.
Revised on: 07 January 2006.
Accepted on: 17 January 2006.
___________________Armenian Journal of Mathematics
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Submitted on: 16 January 2008.
Revised on: 06 April 2008.
Accepted on: 19 May 2008.
___________________Armenian Journal of Mathematics
Submitted on: 07 August 2011.
Revised on: 03 September 2011.
Accepted on: 18 September 2011.
___________________Armenian Journal of Mathematics