1. N. I. Akhizer and I. M. Glazman, Theory of linear operators in Hilbert space (translated from the Russian), Ungar, New York, 1963.
2. L. Collatz, Functional analysis and numerical mathematics (translated from the German), Academic Press, New York-London, 1966.
3. N. Dunford and J. T. Schwarz, Linear operators, Interscience, New York-London, 1958.
4. L. V. Kantorovich and G. P. Akilov, Functional analysis in normed spaces (translated from the Russian), Pergamon, Oxford, 1964.
5. M. A. Krasnosel’skii, G. M. Vainikko, P. P. Zabreiko, Ya. B. Rutitskii and V. Ya. Stetsenko, Approximate solution of operator equations (translated from the Russian), Wolters-Noordhoff, Groningen, 1972.