MITROPOLSKIY, Yu. A.; KHOMA-MOHYL'S'KA, S. H. Conditions for the Existence of Solutions of a Periodic Boundary-Value Problem for an Inhomogeneous Linear Hyperbolic Equation of the Second Order. I. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 7, p. 912–921, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3653. Acesso em: 5 dec. 2025.