SamoilenkoA. M., StepanetsO. I., and ShevchukI. A. “The international Conference „International Workshop on Analysis and Its applications"”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, no. 12, Dec. 2004, p. 1722, https://umj.imath.kiev.ua/index.php/umj/article/view/3880.