1. I. Colojoara and C. Foias, The Theory of Generalized Spectral Operators, Cordon and Breach (N.Y., 1968).
2. N. Dunford and J. T. Schwartz, Linear Operators, Part I: General Theory, Interscience (New York–London, 1958).
3. I. S. Gradstein and I. M. Ryzhik, Tabulated Lists of Integrals, Sums, Series and Products, Nauka (1971) (in Russian).
4. S. Grivaux and M. Roginskaya, Multiplicity of direct sums of operators on Banach spaces, Bull. London Math. Soc., (2009), doi: 10.1112/blms/bdp084 .
5. D. A. Herrero and W. R. Wogen, On multiplicity of T⊕…⊕T, preprint (1987).