BOBOCHKO, V. N. Turning point in a system of differential equations with analytic operator. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 2, p. 147–160, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5343. Acesso em: 17 apr. 2025.