Estimation of eigenvalues of self-adjoint operators

Estimates of the number of eigenvalues are obtained for perturbations of certain self-adjoint and unitary operators in a Hilbert space. In particular, we consider a perturbation of the operator of multiplication by an independent variable inL₂ () andL₂ (0, 1).Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 46, No. 5, pp. 642–648, May, 1994.