SkaskivO. B., and TrusevichО. M. “Relations of Borel Type for Generalizations of Exponential Series”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 53, no. 11, Nov. 2001, pp. 1580-4, https://umj.imath.kiev.ua/index.php/umj/article/view/4379.