Dudkin, M. Ye. “Point Spectrum of the schrödinger Operator With Point Interactions at the Vertices of Regular N-Gons”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 8 (August 25, 2004): 1128–1134. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3827.