  We study 6d N=(2,0) theory of type SU(N) compactified on Riemann surfaces
with finite area, including spheres with fewer than three punctures. The Higgs
branch, whose metric is inversely proportional to the total area of the Riemann
surface, is discussed in detail. We show that the zero-area limit, which gives
us a genuine 4d theory, can involve a Wigner-Inonu contraction of global
symmetries of the six-dimensional theory. We show how this explains why
subgroups of SU(N) can appear as the gauge group in the 4d limit. As a
by-product we suggest that half-BPS codimension-two defects in the
six-dimensional (2,0) theory have an operator product expansion whose operator
product coefficients are four-dimensional field theories.
