Kofanov, V. “Boyanov–Naidenov Problem and the Kolmogorov-Type Inequalities for Functions on the Real Axis”. Ukrains’kyi Matematychnyi Zhurnal, vol. 77, no. 1, Oct. 2025, pp. 14-27, https://doi.org/10.3842/umzh.v77i1.8538.