PTASHNIK, B. I.; SAMOILENKO, A. M. All-Ukrainian scientific conference “New approaches to the solution of differential equations”. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 50, n. 3, p. 454–455, 1998. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4949. Acesso em: 5 dec. 2025.