MURATBEKOV, M.; OTELBAEV, M. On the Existence of a Resolvent and Separability for a Class of Singular Hyperbolic Type Differential Operators on an Unbounded Domain. Eurasian Mathematical Journal, [S. l.], v. 7, n. 1, p. 50–67, 2016. Disponível em: https://emj.enu.kz/index.php/main/article/view/627. Acesso em: 31 oct. 2025.