Voitsekhivs'kyi, V. R. “Jackson-Type Inequalities in the Space $S^p$”.
Ukrains’kyi Matematychnyi Zhurnal
, vol. 55, no. 9, Sept. 2003, pp. 1167-7,
https://umj.imath.kiev.ua/index.php/umj/article/view/3990
.