NIZHNIK, L. P. Inverse eigenvalue problems for nonlocal Sturm-Liouville operators on a star graph. Methods of Functional Analysis and Topology, [S. l.], v. 18, n. 1, p. 68–78, 2012. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/505. Acesso em: 16 dec. 2025.