Hembars’kaS. B. (2003) “Estimates for the Variation of Functions Defined by Double Trigonometric Cosine Series”, Ukrains’kyi Matematychnyi Zhurnal, 55(6), pp. 733-749. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/3949 (Accessed: 24November2024).