Periodic solutions of second-order neutral functional differential systems with time-varying operator and delays. Neliniini Kolyvannya, [S. l.], v. 17, n. 2, p. 180–199, 2014. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/738. Acesso em: 21 jan. 2026.