PetrinaD. Ya. “Spectrum and States of the BCS Hamiltonian With Sources”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 9 (September 25, 2008): 1243–1269. Accessed November 23, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3240.