DANYLYUK, I. M.; PETRYSHYN, R. I.; SAMOILENKO, A. M. Averaging of initial-value and multipoint problems for oscillation systems with slowly varying frequencies and deviated argument. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 59, n. 3, p. 412–430, 2007. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3316. Acesso em: 5 dec. 2025.