Operator theory in finite-dimensional vector spaces.- Perturbation theory in a finite-dimensional space.- to the theory of operators in Banach spaces.- Stability theorems.- Operators in Hilbert spaces.- Sesquilinear forms in Hilbert spaces and associated operators.- Analytic perturbation theory.- Asymptotic perturbation theory.- Perturbation theory for semigroups of operators.- Perturbation of continuous spectra and unitary equivalence.