1. J. Wilkinson, Algebraic eigenvalue problem (Nauka, Moscow, 1970), 584 p.
2. L. Kollatts, Eigenvalue problems (Nauka, Moscow, 1968), 503 p.
3. I. Ts. Gokhbergi, M. G. Krein, Introduction to the Theory of Non-Self-Adjoint Operators in Hilbert Space (Nauka, Moscow, 1965), 448p.
4. V.A. Ilyin, Spectral theory of differential operators (Nauka, Moscow, 1991), 368 p.
5. M.V. Keldysh, On eigenvalues and eigenfunctions of some classes of non-self-adjoint equations (DAN No. 1, Moscow, 1951), 11–14 pp.