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Submitted on: 19 September 2004.
Revised on: 15 October 2004.
Accepted on: 08 November 2004.
Proceedings of the Romanian Academy Series A-Mathematics Physics Technical Sciences Information Science
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Submitted on: 24 May 2013.
Revised on: 16 June 2013.
Accepted on: 09 July 2013.
Proceedings of the Romanian Academy Series A-Mathematics Physics Technical Sciences Information Science
Submitted on: 04 September 2007.
Revised on: 13 October 2007.
Accepted on: 03 November 2007.
Proceedings of the Romanian Academy Series A-Mathematics Physics Technical Sciences Information Science
Submitted on: 26 August 2000.
Revised on: 07 September 2000.
Accepted on: 30 September 2000.
Proceedings of the Romanian Academy Series A-Mathematics Physics Technical Sciences Information Science
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Submitted on: 22 July 2017.
Revised on: 09 August 2017.
Accepted on: 03 September 2017.
Proceedings of the Romanian Academy Series A-Mathematics Physics Technical Sciences Information Science
Submitted on: 27 December 2004.
Revised on: 04 February 2005.
Accepted on: 18 February 2005.
Proceedings of the Romanian Academy Series A-Mathematics Physics Technical Sciences Information Science
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