Kuzhel’S. A., and VavrykovychL. “On Infinite-Rank Singular Perturbations of the Schrödinger Operator”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 4 (April 25, 2008): 487–496. Accessed November 23, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3171.