Ivashchuk, O.V. and Zaderei, P.V. (2011) “On necessary conditions for the convergence of Fourier series”, Ukrains’kyi Matematychnyi Zhurnal, 63(7), pp. 960–968. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/2777 (Accessed: 5 December 2025).