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@misc{MZ_1924__19_167766, title = {Hardy, {G.} {H.,} and {J.} {E.} {Littlewood,} {Solution} of the {Ces\`aro} summability problem for power-series and {Fourier} series}, journal = {Mathematische Zeitschrift}, pages = {67--96}, publisher = {mathdoc}, volume = {19}, year = {1924}, zbl = {49.0232.01}, url = {http://geodesic.mathdoc.fr/item/MZ_1924__19_167766/} }
Hardy, G. H., and J. E. Littlewood, Solution of the Cesàro summability problem for power-series and Fourier series. Mathematische Zeitschrift, Tome 19 (1924), pp. 67-96. http://geodesic.mathdoc.fr/item/MZ_1924__19_167766/