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Submitted on: 09 March 2009.
Revised on: 27 April 2009.
Accepted on: 22 May 2009.
___________________Journal of Mathematics---HINDAWI LTD
Submitted on: 04 July 2019.
Revised on: 08 August 2019.
Accepted on: 26 August 2019.
___________________Journal of Mathematics---HINDAWI LTD
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Submitted on: 27 April 1998.
Revised on: 10 August 1998.
Accepted on: 20 August 1998.
___________________Journal of Mathematics---HINDAWI LTD