1. F. V. Atkinson,Multiparameter spectral theory, Bull. Am. Math. Soc.,74 (1968), pp. 1–27.
2. E.Buzano,Bifurcation analysis of a rod subjected to terminal couple and thrust, to appear on Ann. Mat. Pura Appl.
3. J. Dieudonné,Foundations of Modern Analysis, Academic Press, New York (1960).
4. N. Dunford -J. T. Schwartz,Linear Operators, Part I, Interscience, New York (1958).
5. T. Kato,Perturbation Theory for Linear Operators, Springer-Verlag, New York (1966).