\Bibitem{Zvy86} \by M.~Yu.~Zvyagin \paper Letter to the Editor \jour Mat. Zametki \yr 1986 \vol 40 \issue 6 \pages 771 \mathnet{http://mi.mathnet.ru/mzm5237} \mathscinet{https://mathscinet.ams.org/mathscinet-getitem?mr=887456} \zmath{https://zbmath.org/?q=an:0669.35005|0654.35006} \transl \jour Math. Notes \yr 1986 \vol 40 \issue 6 \pages 933--934 \crossref{https://doi.org/10.1007/BF01158354}