  In this paper, we consider the Sub-Laplacian L which consists of sum of
squares of smooth vector fields that satisfy Hormander's finite rank condition.
We study the Dirichlet problem for this operator on domains that satisfy
certain geometric conditions. For such domains, several key results are
established. These results consist of 1) A reversed Holder inequality for the
Poisson kernel 2) Harmonic measure (corresponding to L) and surface measure (as
well as the H-Perimeter measure) are mutually absolutely continuous 3) A
representation (hence solvability of the Dirichlet problem) for solutions to
the Dirichlet problem.
