A nonsplit extension of a product of free groups by the additive group of a countable division ring

We construct a countable division ring \\(D\\) of characteristic zero, a subgroup \\(G\\leq D^\\times\\) isomorphic to \\(F_2\\times F_2\\), and a nonsplit extension \\(1\\to D^+\\to E\\to G\\to1\\) inducing the action \\(g\\cdot u=gu\\). Both \\(G\\) and \\(E\\) are torsion-free. The factor set is the cup product of two explicitly prescribed free-group derivations. Four commutation equations for the lifts of the free generators force \\(0=1\\) if a section exists. This gives a negative answer to Kourovka Problem 18.76.

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Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-09-14
DOI
https://doi.org/10.5281/zenodo.22751422
Primary Topic
Geometric and Algebraic Topology
Type
preprint
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preprint

A nonsplit extension of a product of free groups by the additive group of a countable division ring

Achyuth Jayadevan
Zenodo (CERN European Organization for Nuclear Research)
Geometric and Algebraic Topology
preprint

A nonsplit extension of a product of free groups by the additive group of a countable division ring

Achyuth Jayadevan
preprint en

Abstract

We construct a countable division ring \(D\) of characteristic zero, a subgroup \(G\leq D^\times\) isomorphic to \(F_2\times F_2\), and a nonsplit extension \(1\to D^+\to E\to G\to1\) inducing the action \(g\cdot u=gu\). Both \(G\) and \(E\) are torsion-free. The factor set is the cup product of two explicitly prescribed free-group derivations. Four commutation equations for the lifts of the free generators force \(0=1\) if a section exists. This gives a negative answer to Kourovka Problem 18.76.

Zenodo (CERN European Organization for Nuclear Research)
Manipal Academy of Higher Education (IN)
Geometric and Algebraic Topology
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