Boichuk О. A.; CHUIKO, S. M. Periodic solutions of autonomous systems with pulse influence in critical cases. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 11, p. 1478–1484, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5538. Acesso em: 6 dec. 2025.