  This paper deals with some analytic aspects of GG system introduced by
I.M.Gelfand and M.I.Graev: we compute the dimension of the solution space of GG
system over the field of functions meromorphic and periodic with respect to a
lattice. We describe the monodromy invariant subspace of the solution space. We
give a connection formula between a pair of bases consisting of $\Gamma$-series
solutions of GG system associated to a pair of regular triangulations adjacent
to each other in the secondary fan.
