Grona , V.L. (1991) “Uniform convergence of the Fourier spherical sums differentiated by the function”, Ukrains’kyi Matematychnyi Zhurnal, 43(1), pp. 47–53. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/9304 (Accessed: 17 February 2026).