Decidability of fundamental groups of Einstein 4-manifolds
Determine whether the fundamental groups of general Einstein 4-manifolds form a sufficiently special class for the isomorphism problem to be decidable.
References
Whether the fundamental groups of general Einstein 4-manifolds are sufficiently special as to similarly tip the scales in favor of decidability is still apparently an open problem — and one that is surely worth settling!
— An Overview of Einstein 4-Manifolds
(2609.03033 - LeBrun, 2 Sep 2026) in Section 4, final paragraph before Section 5