Abstract
We consider the Szegő projector and the partial inverse for the $\square_b$-operator defined by a strictly pseudoconvex CR-structure on a compact manifold. In particular we study the dependence on the CR-structure in the construction of Beals and Greiner of an approximate projective and partial inverse for $\square_b$. Parametrices for some operators introduced in [Ep] are constructed. This entails the analysis of the inverses for certain classes of convolution operators on the Heisenberg group.
