Geodesic
On Cesàro Means of Double Trigonometric Fourier Series
Matematičeskie zametki, Tome 74 (2003) no. 4, pp. 502-507 
U. Goginava. On Cesàro Means of Double Trigonometric Fourier Series. Matematičeskie zametki, Tome 74 (2003) no. 4, pp. 502-507. http://geodesic.mathdoc.fr/item/MZM_2003_74_4_a2/
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     title = {On {Ces\`aro} {Means} of {Double} {Trigonometric} {Fourier} {Series}},
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     url = {http://geodesic.mathdoc.fr/item/MZM_2003_74_4_a2/}
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Voir la notice de l'article provenant de la source Math-Net.Ru

Zhizhiashvili studied questions associated with the approximation properties of Cesàro means of trigonometric Fourier series for functions of two variables in the spaces $H^\omega$. It is proved here that the corresponding estimate cannot be improved for $p = 1$ or $p=\infty$.

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[2] Zigmund A., Trigonometricheskie ryady, T. 1, Mir, M., 1965

[3] Zhizhiashvili L. V., Nekotorye voprosy teorii trigonometricheskikh ryadov Fure i ikh sopryazhennykh, Izd. TGU, Tbilisi, 1993

[4] Zygmund A., “Sur la summabilité des series de Fourier des fonctions verifiant la condition de Lipschitz”, Bull. Acad. Polon. Sci. Ser. Math. Astronom. Phys., 1925, 1–9

[5] Zygmund A., “A remark on conjugate series”, PLMS, 34 (1932), 392–400 | DOI | MR | Zbl