A Low-Dimensional Counterexample to the HK-Conjecture

We provide a counterexample to the HK-conjecture using the flat manifold odometers constructed by Deeley. Deeley’s counterexample uses an odometer built from a flat manifold of dimension 9 and an expansive self-cover. We strengthen this result by showing that for each dimension $d\ge 4$ there is a counterexample to the HK-conjecture built from a flat manifold of dimension $d$. Moreover, we show that this dimension is minimal, as if $d\le 3$ the HK-conjecture holds for the associated odometer. We also discuss implications for the stable and unstable groupoid of a Smale space.