Submitted on: 06 July 2017.
Revised on: 28 July 2017.
Accepted on: 07 August 2017.
___________________Bulletin of the Karaganda University-Mathematics
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Submitted on: 12 March 2002.
Revised on: 02 June 2002.
Accepted on: 21 July 2002.
___________________Bulletin of the Karaganda University-Mathematics
Submitted on: 04 November 2013.
Revised on: 02 January 2014.
Accepted on: 30 January 2014.
___________________Bulletin of the Karaganda University-Mathematics
Submitted on: 23 July 2003.
Revised on: 29 September 2003.
Accepted on: 10 November 2003.
___________________Bulletin of the Karaganda University-Mathematics
Submitted on: 20 December 2022.
Revised on: 09 March 2023.
Accepted on: 04 May 2023.
___________________Bulletin of the Karaganda University-Mathematics