The averaging of nonlinear oscillation systems of the highest approximation with a delay. Neliniini Kolyvannya, [S. l.], v. 5, n. 1, p. 77–85, 2002. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/202. Acesso em: 22 jan. 2026.