Sobriety of the Scott space of the rational line

Determine whether the Scott space of the lattice of open subsets of the rational line \(\mathbb{Q}\) is sober, equivalently, whether the Hoare power space \(H(\mathbb{Q})\) is co-sober.

Background

The paper establishes a general equivalence for every T0T_0-space XX: the Hoare power space H(X)H(X) is co-sober if and only if the Scott space of the lattice O(X)\mathcal{O}(X) of open subsets of XX is sober. The authors then note that He and Zhao posed the specific question of whether this Scott space is sober when X=QX=\mathbb{Q}, the rational line. The construction developed in the paper produces a different countable metrizable counterexample and therefore does not resolve the rational-line case.

References

He and Zhao also asked whether $\SigmaO(\mathbb{Q})$ is sober for the rational line $\mathbb{Q}$. The construction above does not decide that more specific question. By Theorem~\ref{thm:bridge}, it is equivalent to asking whether $H(\mathbb{Q})$ is co-sober.

— A countable metric space whose Hoare power space is not co-sober  (2610.05868 - Xu et al., 5 Oct 2026) in Section 5, Concluding remarks