Babenko, V.F. (2019) “One inequality of the Landau – Kolmogorov type for periodic functions of two variable”, Ukrains’kyi Matematychnyi Zhurnal, 71(2), pp. 158–167. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/1428 (Accessed: 5 December 2025).