PETROVSKII, Ya. B. Periodic solutions of Quasilinear Hyperbolic integro-differential equations of second order. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 11, p. 1572–1575, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5211. Acesso em: 14 apr. 2025.