  We prove a conjecture of Ambrus, Ball and Erd\'{e}lyi that equally spaced
points maximize the minimum of discrete potentials on the unit circle whenever
the potential is of the form \sum_{k=1}^n f(d(z,z_k)), where $f:[0,\pi]\to
[0,\infty]$ is non-increasing and strictly convex and $d(z,w)$ denotes the
geodesic distance between $z$ and $w$ on the circle.
