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Submitted on: 15 August 2013.
Revised on: 09 December 2013.
Accepted on: 14 January 2014.
___________________Filomat---UNIV NIS, FAC SCI MATH
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Submitted on: 12 July 2012.
Revised on: 19 October 2012.
Accepted on: 14 December 2012.
___________________Filomat---UNIV NIS, FAC SCI MATH
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Submitted on: 12 November 2022.
Revised on: 13 December 2022.
Accepted on: 29 January 2023.
___________________Filomat---UNIV NIS, FAC SCI MATH
Submitted on: 31 January 1999.
Revised on: 25 April 1999.
Accepted on: 17 May 1999.
___________________Filomat---UNIV NIS, FAC SCI MATH
Submitted on: 22 October 2017.
Revised on: 29 December 2017.
Accepted on: 16 January 2018.
___________________Filomat---UNIV NIS, FAC SCI MATH
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