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Decidability of residual finiteness for one‑relator groups

Determine whether residual finiteness is a decidable property in the class of one‑relator groups; that is, develop an algorithm that, given a one‑relator presentation F(S)/<<w>>, decides whether the group is residually finite.

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Background

Residual finiteness is a weaker property than free‑by‑cyclic; numerous subclasses of one‑relator groups are known to be residually finite, and many (e.g., Baumslag–Solitar groups) are not. The authors point out that the existence of a deciding algorithm across the full class remains unsettled.

Progress on this would bridge algorithmic group theory and profinite methods and impact the classification of one‑relator groups.

References

Residual finiteness is, in general, a significantly weaker property than being free-by-cyclic, even in the class of one-relator groups. It remains an open problem whether residual finiteness is decidable for one-relator groups.

The theory of one-relator groups: history and recent progress (2501.18306 - Linton et al., 30 Jan 2025) in Section 4.5 (Free‑by‑cyclic one‑relator groups)