Geodesic
Estimation of functions orthogonal to piecewise constant functions in terms of the second modulus of continuity
Zapiski Nauchnykh Seminarov POMI, Investigations on linear operators and function theory. Part 45, Tome 456 (2017), pp. 96-106 Cet article a éte moissonné depuis la source Math-Net.Ru

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The article is concerned with the question about the exact constant $W_2^*$ in the inequality $\|f\|\le K\cdot\omega_2(f,\,1)$ for bounded functions $f$ with the property $$ \int_k^{k+1}f(x)\,dx=0,\qquad k\in\mathbb Z. $$ The approach suggested made it possible to reduce the known range for the desired constant as well as the set of functions involved in the extremal problem for finding the constant in question. It is shown that $W_2^*$ also turns out to be the exact constant in a related Jackson–Stechkin type inequality. 
@article{ZNSL_2017_456_a6,
     author = {L. N. Ikhsanov},
     title = {Estimation of functions orthogonal to piecewise constant functions in terms of the second modulus of continuity},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {96--106},
     year = {2017},
     volume = {456},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2017_456_a6/}
}
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L. N. Ikhsanov. Estimation of functions orthogonal to piecewise constant functions in terms of the second modulus of continuity. Zapiski Nauchnykh Seminarov POMI, Investigations on linear operators and function theory. Part 45, Tome 456 (2017), pp. 96-106. http://geodesic.mathdoc.fr/item/ZNSL_2017_456_a6/

[1] Yu. Kryakin, Whitney's theorem for oscillating on $\mathbb R$ functions, arXiv: math/0612442v1[math.CA]

[2] O. L. Vinogradov, L. N. Ikhsanov, “Otsenki normy funktsii, ortogonalnoi kusochno-postoyannym, cherez moduli nepreryvnosti vysokikh poryadkov”, Vestnik SPbGU, Ser. 1, 3(61):1 (2016), 8–12 | MR

[3] L. N. Ikhsanov, Otsenka normy funktsii, ortogonalnoi kusochno-postoyannym, cherez vtoroi modul nepreryvnosti. Podrobnoe izlozhenie, Preprint No 5, , POMI, 2017 http://www.pdmi.ras.ru/preprint/2017/rus-2017.html