NORKIN , S. B. Singular single-point problem for the nonlinear delay system. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 4, p. 459–469, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9181. Acesso em: 6 dec. 2025.