Doronin, V.G. and Ligun, A.A. (1994) “Exact constant in the Jackson inequality in the space L2”, Ukrains’kyi Matematychnyi Zhurnal, 46(9), pp. 1261–1265. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5643 (Accessed: 10 April 2025).