YAKOVETS, V. P. Asymptotics of the general solution to a linear singularly perturbed system of second-order differential equations with degeneracy. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 4, p. 561–575, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5843. Acesso em: 5 dec. 2025.