ASSANOVA, A. T.; DZHUMABAEV, D. S. Periodic solutions of systems of hyperbolic equations bounded on a plane. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 56, n. 4, p. 562–572, 2004. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3777. Acesso em: 5 dec. 2025.