Hembars’kaS. B., and ZadereiP. V. “Estimations of the Integral of Modulus for Mixed Derivatives of the Sum of Double Trigonometric Series”. Ukrains’kyi Matematychnyi Zhurnal 68, no. 7 (July 25, 2016): 908-921. Accessed December 9, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1890.