Doronin V. G., and Ligun A.A. “Problem of Amplification of the Jackson-Type Inequalities ”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 4 (April 17, 1992): 475-480. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/7888.