Pivovarchik, V. N., and O. P. Boyko. “Inverse Spectral Problem for a Star Graph of Stieltjes Strings”. Methods of Functional Analysis and Topology 14, no. 2 (June 25, 2008): 159–167. Accessed December 18, 2025. https://zen.imath.kiev.ua/index.php/mfat/article/view/379.