“Low and High Frequency Convergence of the Spectrum of Some Self-Adjoint Compact Operator that Depends on a Small Parameter” (2001) Neliniini Kolyvannya, 4(2), pp. 241–251. Available at: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/168 (Accessed: 22 January 2026).