On the spectrum of general second order operators

This result has been extended to other self ad joint problems for second order operators. See [2], [3], and [ó]. The purpose of this note is to show that the same technique locates the spectrum of a nonself adjoint problem in a half-plane. Such a result is of interest in investigating stability, where one needs to know whether there is any spectrum in the half-plane Re X ^ 0. In a bounded domain D we consider the differential equation