The one-ended subgroup characterization for inaccessible finitely generated groups

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Let GG be a finitely generated group and let HH be a subgroup of GG. Say that HH is 1-ended in GG when it has one end relative to GG.

The one-ended subgroup characterization. The subgroup HH of the finitely generated group GG is 1-ended in GG if and only if for each splitting A∗CBA\ast_C B of GG, where A≠C≠BA\ne C\ne B and CC is finite, HH is a subgroup of a conjugate of AA or BB.

This question is raised in the context of inaccessible finitely generated groups; the paper asks what can be said about such groups. The source provides no resolution of the characterization.

References

Primary source

Michael Mihalik, “A Manual for Ends, Semistability and Simple Connectivity at Infinity for Groups and Spaces”, arXiv:2507.17060 (2026).

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