Geodesic
Sharp inequality of Jackson--Stechkin type and widths of functional classes in the space $L_2$
Eurasian mathematical journal, Tome 5 (2014) no. 1, pp. 122-134.

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For classes of differentiable periodic functions, defined by means of generalized moduli of continuity $\Omega_m(f,t)$, satisfying the condition $$ \left(\int_0^h\Omega_m^{2/m}(f^{(r)},t)dt\right)\leqslant\Phi(h), $$ where $m\in\mathbb{N}$, $r\in\mathbb{Z}_+$, $h>0$ and $\Phi$ is a given majorant, under certain restrictions on the majorant, the exact values of various $n$-widths in the space $L_2$ are calculated. 
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M. R. Langarshoev. Sharp inequality of Jackson--Stechkin type and widths of functional classes in the space $L_2$. Eurasian mathematical journal, Tome 5 (2014) no. 1, pp. 122-134. http://geodesic.mathdoc.fr/item/EMJ_2014_5_1_a4/

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