PETRYSHYN, Ya. R.; SAMOILENKO, A. M. Boundary-value problems with parameters for a multifrequency oscillation system. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 4, p. 581–589, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5034. Acesso em: 5 dec. 2025.