  The constraints of N=2 supersymmetry, in combination with several other quite
general assumptions, have recently been used to show that N=2 supersymmetric
Yang-Mills theory has a low energy quantum parameter space symmetry
characterised by the discrete group $\gu$. We show that if one also assumes the
commutativity of renormalization group flow with the action of this group on
the complexified coupling constant $\ta$, then this is sufficient to determine
the non-perturbative $\beta$-function, given knowledge of its weak coupling
behaviour. The result coincides with the outcome of direct calculations from
the Seiberg-Witten solution.
