  We consider scattering by an abstract compactly supported perturbation in
R^n. To include the traditional cases of potential, obstacle and metric
scattering without going into their particular nature we adopt the "black box"
formalism developed jointly with Sjostrand [23]. It is quite likely that one
could extend the results presented here to the case of non-compactly supported
perturbation as well - see [21] for a natural generalization of "black box"
perturbations.
