Molyboga, V. M., and V. A. Mikhailets. “Hill’s Potentials in Hörmander Spaces and Their Spectral Gaps”. Methods of Functional Analysis and Topology 17, no. 3 (September 25, 2011): 235–243. Accessed February 4, 2026. https://zen.imath.kiev.ua/index.php/mfat/article/view/489.