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MR 0126115
[3] HARDY G. H., LITTLEWOOD J. E.:
A convergence criterion for Fourier series. Math. Z. 28 (1928), 614-634.
MR 1544980
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[7] ULJANOV P. L.:
On the absolute and uniform convergence of Fourier series. (Russian), Mat. Sb. 72 (1967), 193-225.
MR 0206613