Key points are not available for this paper at this time.
One of the interesting developments in spectral theory recently has been the application of a new formula for a function j{H) of a self-adjoint operator H by Helffer and Sjostrand 8. This formula, equation (5) below, depends upon the use of almost analytic extensions of functions initially defined on the real line, an idea due
E. B. Davies (Tue,) studied this question.