A description of the sets of Lebesque points and points of summability for a Fourier series
Sbornik. Mathematics, Tome 74 (1993) no. 1, pp. 111-118 Cet article a éte moissonné depuis la source Math-Net.Ru

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The set of Lebesgue points of a locally integrable function on $N$-dimensional Euclidean space $\mathbf R^N$, $N\geqslant1$, is an $F_{\sigma\delta}$-set of full measure. In this article it is shown that every $F_{\sigma\delta}$-set of full measure is the set of Lebesgue points of some measurable bounded function, and, further, that a set with these properties is the set of points of convergence and nontangential (stable) convergence of a singular integral of convolution type: $$ \varphi_\varepsilon\ast f(x), \quad \varphi_\varepsilon(t)=\varepsilon^{-N}\varphi(t/\varepsilon)\in L(\mathbf R^N), \quad \varepsilon\to+0, $$ for some measurable bounded function $f$. On the basis of this result the set of points of summability of a multiple Fourier series by methods of Abel, Riesz, and Picard types is described.
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A. M. Diyachkov. A description of the sets of Lebesque points and points of summability for a Fourier series. Sbornik. Mathematics, Tome 74 (1993) no. 1, pp. 111-118. http://geodesic.mathdoc.fr/item/SM_1993_74_1_a8/

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