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Submitted on: 27 May 2008.
Revised on: 30 June 2008.
Accepted on: 28 July 2008.
Lithuanian Mathematical Journal
Submitted on: 17 March 2009.
Revised on: 13 April 2009.
Accepted on: 29 April 2009.
Lithuanian Mathematical Journal
Submitted on: 07 October 1998.
Revised on: 20 October 1998.
Accepted on: 01 November 1998.
Lithuanian Mathematical Journal
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