L. P. Nizhnik and J. F. Brasche, “One-dimensional Schrödinger operators with general point interactions”, MFAT, vol. 19, no. 1, pp. 4–15, Mar. 2013, Accessed: Dec. 16, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/531