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Submitted on: 16 June 2002.
Revised on: 16 July 2002.
Accepted on: 30 July 2002.
___________________Annals of Mathematical Sciences and Applications
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Submitted on: 19 February 2017.
Revised on: 12 March 2017.
Accepted on: 08 May 2017.
___________________Annals of Mathematical Sciences and Applications
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Submitted on: 02 June 2015.
Revised on: 30 August 2015.
Accepted on: 03 October 2015.
___________________Annals of Mathematical Sciences and Applications
Submitted on: 20 June 2005.
Revised on: 22 August 2005.
Accepted on: 17 October 2005.
___________________Annals of Mathematical Sciences and Applications
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