  In the setting of exponential investors and uncertainty governed by Brownian
motions we first prove the existence of an incomplete equilibrium for a general
class of models. We then introduce a tractable class of exponential-quadratic
models and prove that the corresponding incomplete equilibrium is characterized
by a coupled set of Riccati equations. Finally, we prove that these
exponential-quadratic models can be used to approximate the incomplete models
we studied in the first part.
