KLYUCHNYK, I. H. Asymptotic solutions of a system of differential equations with multiple turning point. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 11, p. 1516–1530, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3118. Acesso em: 5 dec. 2025.