Submitted on: 30 May 2019.
Revised on: 23 September 2019.
Accepted on: 24 October 2019.
___________________Bulletin of Mathematical Analysis and Applications
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Submitted on: 20 November 2014.
Revised on: 21 February 2015.
Accepted on: 31 March 2015.
___________________Bulletin of Mathematical Analysis and Applications
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Submitted on: 19 September 2011.
Revised on: 07 January 2012.
Accepted on: 27 February 2012.
___________________Bulletin of Mathematical Analysis and Applications
Submitted on: 16 April 2006.
Revised on: 07 June 2006.
Accepted on: 17 June 2006.
___________________Bulletin of Mathematical Analysis and Applications
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Submitted on: 09 March 2007.
Revised on: 28 May 2007.
Accepted on: 10 July 2007.
___________________Bulletin of Mathematical Analysis and Applications
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