V. M. Molyboga and V. A. Mikhailets, “Spectral gaps of one-dimensional Schrödinger operators with singular periodic potentials”, MFAT, vol. 15, no. 1, pp. 31–40, Mar. 2009, Accessed: Feb. 04, 2026. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/406