Existence of a countable number of cycles in hyperbolic systems of differential equations with transformed argument. Neliniini Kolyvannya, [S. l.], v. 18, n. 1, p. 71–78, 2015. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/770. Acesso em: 21 jan. 2026.