  We investigate S^3/Z_n partition function of N = 2 supersymmetric gauge
theories. A gauge theory on the orbifold has degenerate vacua specified by the
holonomy. The partition function is obtained by summing up the contributions of
saddle points with different holonomies. An appropriate choice of the phase of
each contribution is essential to obtain the partition function. We determine
the relative phases in the holonomy sum in a few examples by using duality to
non-gauge theories. In the case of odd n the phase factors can be absorbed by
modifying a single function appearing in the partition function.
