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Submitted on: 26 August 2011.
Revised on: 25 November 2011.
Accepted on: 18 January 2012.
___________________ACTA INFORMATICA---SPRINGER
http://reply.papertrans.cn/1/4/353/353-29.png
Submitted on: 21 August 2004.
Revised on: 24 September 2004.
Accepted on: 27 October 2004.
___________________ACTA INFORMATICA---SPRINGER