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A group-theoretic framework for low-dimensional topology, or: how not to study low-dimensional topology?

Sarah Blackwell, Robion Kirby, Michael Klug, Vincent Longo and Benjamin Ruppik

Algebraic & Geometric Topology 25 (2025) 4667–4718
Abstract

A correspondence, by way of Heegaard splittings, between closed, oriented 3-manifolds and pairs of surjections from a surface group to a free group has been studied by Stallings, Jaco and Hempel. This correspondence, by way of trisections, was recently extended by Abrams, Gay and Kirby to the case of smooth, closed, connected, oriented 4-manifolds. We unify these perspectives and generalize this correspondence to the case of links in closed, oriented 3-manifolds and links of knotted surfaces in smooth, closed, connected, oriented 4-manifolds. The algebraic manifestations of these four subfields of low-dimensional topology (3-manifolds, 4-manifolds, knot theory and knotted surface theory) are all strikingly similar, and this correspondence perhaps elucidates some unique character of low-dimensional topology.

Keywords
splitting homomorphisms, group trisections, tangles in handlebodies, links in 3-manifolds, knotted surfaces in 4-manifolds, surface groups, free groups, Stallings folding
Mathematical Subject Classification
Primary: 57K40
Secondary: 20F05, 57M05
References
Publication
Received: 9 August 2023
Revised: 24 April 2024
Accepted: 26 May 2024
Published: 20 November 2025
Authors
Sarah Blackwell
Department of Mathematics
University of Virginia
Charlottesville, VA
United States
https://seblackwell.com
Robion Kirby
Department of Mathematics
University of California, Berkeley
Berkeley, CA
United States
https://math.berkeley.edu/~kirby
Michael Klug
Department of Mathematics
University of Chicago
Chicago, IL
United States
https://mathematics.uchicago.edu/people/profile/michael-klug
Vincent Longo
Department of Mathematics
University of Connecticut
Storrs, CT
United States
https://math.uconn.edu/person/vincent-longo
Benjamin Ruppik
Heinrich-Heine-Universität
Düsseldorf
Germany
https://bruppik.de

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