Pivovarchik, V.N. and Martinyuk, O. (2010) “Spectral problem for figure-of-eight graph of Stieltjes strings”, Methods of Functional Analysis and Topology, 16(4), pp. 349–358. Available at: https://zen.imath.kiev.ua/index.php/mfat/article/view/462 (Accessed: 16 December 2025).