MOLYBOGA, V. M. Estimates for periodic eigenvalues of the differential operator $(-1)^md^2m/dx^2m+V$ with $V$-distribution. Methods of Functional Analysis and Topology, [S. l.], v. 9, n. 2, p. 163–178, 2003. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/212. Acesso em: 17 dec. 2025.