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Submitted on: 30 September 2016.
Revised on: 20 January 2017.
Accepted on: 19 February 2017.
___________________Journal of Siberian Federal University-Mathematics & Physics
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Submitted on: 14 December 2019.
Revised on: 03 February 2020.
Accepted on: 17 March 2020.
___________________Journal of Siberian Federal University-Mathematics & Physics
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