\Bibitem{Rol19} \by P.~V.~Roldugin \paper Letter to the Editors \jour Diskr. Mat. \yr 2019 \vol 31 \issue 4 \pages 128 \mathnet{http://mi.mathnet.ru/dm1600} \crossref{https://doi.org/10.4213/dm1600} \mathscinet{https://mathscinet.ams.org/mathscinet-getitem?mr=4043288}