B. I. Ptashnik and A. M. Samoilenko, “All-Ukrainian scientific conference ‘New approaches to the solution of differential equations’”, Ukr. Mat. Zhurn., vol. 50, no. 3, pp. 454–455, Mar. 1998, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4949