\Bibitem{Gri83} \by M.~Zh.~Grigoryan \paper Convergence in the metric of $L_p$, $0<p<1$, of spherical partial sums of double Fourier series \jour Mat. Zametki \yr 1983 \vol 33 \issue 4 \pages 517--528 \mathnet{http://mi.mathnet.ru/mzm5687} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=704439} \zmath{https://zbmath.org/?q=an:0516.42021} \transl \jour Math. Notes \yr 1983 \vol 33 \issue 4 \pages 264--270 \crossref{https://doi.org/10.1007/BF01157057} \isi{https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=Publons&SrcAuth=Publons_CEL&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=A1983RS92800020}