KHRABUSTOVSKYI, V. Eigenfunction expansions associated with an operator differential equation non-linearly depending on a spectral parameter. Methods of Functional Analysis and Topology, [S. l.], v. 20, n. 1, p. 68–91, 2014. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/568. Acesso em: 16 dec. 2025.