Comparison Principles for subelliptic equations of Monge-Ampere type
  We present two comparison principles for viscosity sub- and supersolutions of Monge-Ampere-type equations associated to a family of vector fields. In particular, we obtain the uniqueness of a viscosity solution to the Dirichlet problem for the equation of prescribed horizontal Gauss curvature in a Carnot group. 
Martino Bardi, Paola Mannucci