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Submitted on: 04 February 2009.
Revised on: 17 February 2009.
Accepted on: 10 March 2009.
Open Mathematics---DE GRUYTER POLAND SP Z O O
Submitted on: 18 October 1999.
Revised on: 04 November 1999.
Accepted on: 28 November 1999.
Open Mathematics
Submitted on: 20 July 2005.
Revised on: 14 August 2005.
Accepted on: 30 August 2005.
Open Mathematics---DE GRUYTER POLAND SP Z O O
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