“Low and High Frequency Convergence of the Spectrum of Some Self-Adjoint Compact Operator that Depends on a Small Parameter”, НК, vol. 4, no. 2, pp. 241–251, Jun. 2001, Accessed: Jan. 22, 2026. [Online]. Available: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/168