PETRYSHYN, Ya. R.; SAMOILENKO, A. M. Averaging method in multipoint problems of the theory of nonlinear oscillations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 8, p. 1096–1103, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5253. Acesso em: 6 dec. 2025.