Notes on the Sigma invariants

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arxiv 1204.0214 v2 pith:FNTE3S4H submitted 2012-04-01 math.GR

Ralph Strebel This is my paper · ORCID

classification math.GR

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Memoir on the Sigma invariants and their applications, version 2

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On the BNSR invariants of link groups
math.GT 2026-06 unverdicted novelty 7.0 of 10

For multi-component links the commutator subgroup of the link group is finitely generated precisely when the link is the Hopf link; a ribbon 2-knot exists whose group has non-symmetric BNS invariant.
Actions with a strong fundamental domain and Sigma invariants of groups
math.GR 2026-06 unverdicted novelty 6.0 of 10

A general criterion on group actions with contractible strong fundamental domains implies homological Sigma invariants are empty or dense in the character sphere, applied to new families including pure symmetric autom...