Volchkov, V. V., and I. M. Savost’yanova. 2015. “Smoothing of the Singularities of Functions Whose Integrals over the Balls on a Sphere Are Zero”. Ukrains’kyi Matematychnyi Zhurnal 67 (2), 272-78. https://umj.imath.kiev.ua/index.php/umj/article/view/1979.