\Bibitem{1} \paper Andrey Izmailovich Subbotin \serial Trudy Inst. Mat. i Mekh. UrO RAN \yr 2021 \vol 27 \issue 3 \pages 7--11 \mathnet{http://mi.mathnet.ru/timm1834} \crossref{https://doi.org/10.21538/0134-4889-2021-27-3-7-11} \elib{https://elibrary.ru/item.asp?id=46502686}