L. P. Nizhnik, “Inverse eigenvalue problems for nonlocal Sturm-Liouville operators on a star graph”, MFAT, vol. 18, no. 1, pp. 68–78, Mar. 2012, Accessed: Dec. 16, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/505