DoroninV. G., & LigunA. A. (1994). Exact constant in the Jackson inequality in the space <i>L</i><sub>2</sub&gt;. Ukrains’kyi Matematychnyi Zhurnal, 46(9), 1261–1265. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/5643