Funding for this research was provided by:
The development program for the Scientific and Educational Mathematical Center of the Volga Federal District (075-02-2020-1478)
Russian Government Program of Competitive Growth at Kazan Federal University.
The development program for the Scientific and Educational Mathematical Center of the Volga Federal District (075-02-2020-1478)
Article History
Received: 7 February 2020
Accepted: 21 April 2021
First Online: 26 May 2021