  We study the $\NN=2$ string theory or the $\NN=4$ topological string on the
deformed CHS background. That is, we consider the $\NN=2$ minimal model coupled
to the $\NN=2$ Liouville theory. This model describes holographically the
topological sector of Little String Theory. We use degenerate vectors of the
respective $\NN=2$ Verma modules to find the set of BRST cohomologies at ghost
number zero--the ground ring, and exhibit its structure. Physical operators at
ghost number one constitute a module of the ground ring, so the latter can be
used to constrain the S-matrix of the theory. We also comment on the
inequivalence of BRST cohomologies of the $\NN=2$ string theory in different
pictures.
