ALIEV, A. R. On the Solvability of a Fourth-Order Operator-Differential Equation with Multiple Characteristic. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 66, n. 5, p. 699–707, 2014. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2171. Acesso em: 5 dec. 2025.