Submitted on: 27 May 2009.
Revised on: 03 August 2009.
Accepted on: 16 September 2009.
___________________Bulletin of the Malaysian Mathematical Sciences Society
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Submitted on: 16 November 2008.
Revised on: 16 February 2009.
Accepted on: 18 March 2009.
___________________Bulletin of the Malaysian Mathematical Sciences Society
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Submitted on: 10 June 2013.
Revised on: 31 July 2013.
Accepted on: 04 September 2013.
___________________Bulletin of the Malaysian Mathematical Sciences Society
Submitted on: 28 April 2012.
Revised on: 06 June 2012.
Accepted on: 02 August 2012.
___________________Bulletin of the Malaysian Mathematical Sciences Society
Submitted on: 18 August 2012.
Revised on: 25 October 2012.
Accepted on: 12 November 2012.
___________________Bulletin of the Malaysian Mathematical Sciences Society