Adian–Rabin families of balanced presentations
Determine whether there exists an Adian–Rabin family consisting entirely of balanced finite group presentations.
References
A longstanding open problem asks whether there exists an Adian--Rabin family consisting entirely of balanced presentations.
— Small undecidable groups and unrecognizable 4-manifolds
(2609.10461 - Kegel et al., 9 Sep 2026) in Section 1, subsection “Algebra”