KOSHMANENKO, V. D. A variant of the inverse negative eigenvalues problem in singular perturbation theory. Methods of Functional Analysis and Topology, [S. l.], v. 8, n. 1, p. 49–69, 2002. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/176. Acesso em: 18 dec. 2025.