Key points are not available for this paper at this time.
An elementary model of the gravitational field in the presence of external sources is studied. This model has positivity requirements, invariance under transformations, and nonlinear equations of motion, all of which are analogs of similar properties in the full theory. The classical solutions of the "free" version of this model exhibit singularities, but these are removed in the quantum theory.
Klauder et al. (Wed,) studied this question.