Submitted on: 29 June 2008.
Revised on: 07 August 2008.
Accepted on: 21 August 2008.
___________________Asian-European Journal of Mathematics
Submitted on: 21 August 2006.
Revised on: 08 October 2006.
Accepted on: 20 November 2006.
___________________Asian-European Journal of Mathematics
Submitted on: 22 March 2016.
Revised on: 12 July 2016.
Accepted on: 31 August 2016.
___________________Asian-European Journal of Mathematics
Submitted on: 23 June 2007.
Revised on: 15 September 2007.
Accepted on: 12 October 2007.
___________________Asian-European Journal of Mathematics
Submitted on: 23 July 2014.
Revised on: 21 August 2014.
Accepted on: 17 September 2014.
___________________Asian-European Journal of Mathematics
Submitted on: 20 September 2011.
Revised on: 18 October 2011.
Accepted on: 30 October 2011.
___________________Asian-European Journal of Mathematics
Submitted on: 11 March 2015.
Revised on: 16 May 2015.
Accepted on: 22 June 2015.
___________________Asian-European Journal of Mathematics
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http://reply.papertrans.cn/1/29/2854/2854-29.png
Submitted on: 23 June 2016.
Revised on: 09 August 2016.
Accepted on: 25 September 2016.
___________________Asian-European Journal of Mathematics