On uniform approximation of functions by Fourier sums

This paper studies traditional problems on uniform approximation of a continuous $2\pi$-periodic function $f$ by its $n$th Fourier sums $S_n(f)$. To this end the deviation $\|f-S_n(f)\|_{C_{2\pi}}$ is estimated in terms of some new functional characteristics. As an application of the estimates a number of known results (due to Lebesgue, Salem, Stechkin, Ul'yanov, Oskolkov, and others) are obtained.
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