  General two-dimensional pure dilaton-gravity can be discussed in a unitary
way by introducing suitable field redefinitions. The new fields are directly
related to the original spacetime geometry and in the canonical picture they
generalize the well-known geometrodynamical variables used in the discussion of
the vacuum dilatonic black hole. So the model can be quantized using the
techniques developed for the latter case. The resulting quantum theory
coincides with the quantum theory obtained imposing the Birkhoff theorem at the
classical level.
