Makarov, V. L., and N.M. Romaniuk. 2025. “The FD-Method for an Eigenvalue Problem in a Case Where the Base Problem Has Eigenvalues of Arbitrary Multiplicities in a Hilbert Space”. Reports of the National Academy of Sciences of Ukraine, no. 5 (February). Kyiv, Ukraine:26-34. https://doi.org/10.15407/dopovidi2015.05.026.