LigunA. A., and ChernayaE. V. “On Extremal Problems on Classes of Functions Defined by Integral Moduli of Continuity”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 11 (November 25, 1997): 1499–1503. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5148.