LinchukN. E., and LinchukS. S. “On Some Properties of Gelfond – Leontiev Generalized Integration Operators”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 63, no. 1, Jan. 2011, pp. 61-68, https://umj.imath.kiev.ua/index.php/umj/article/view/2698.