Exotic presentations of quaternion groups and Wall's D2 problem

Tommy Hofmann; John Nicholson

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arXiv · 2507.15999

Exotic presentations of quaternion groups and Wall's D2 problem

Tommy Hofmann·John Nicholson

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Abstract

The D2 problem of C. T. C. Wall asks whether every finite cohomologically 2-dimensional CW-complex is homotopy equivalent to a finite 2-complex. Several potential counterexamples have been proposed, the longest standing of which is a CW-complex constructed by Cohen and Dyer whose fundamental group is a quaternion group of order 32. We show that this CW-complex is homotopy equivalent to the presentation 2-complex of a presentation constructed by Mannan-Popiel, thus showing it is not a counterexample to the D2 problem. We next introduce an infinite family of presentations for a quaternion group of order $4n$ and prove that they achieve homotopy types which are not achieved by the presentations of Mannan-Popiel.

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Tommy Hofmann, John Nicholson. 2025-07-21. Exotic presentations of quaternion groups and Wall's D2 problem. https://arxiv.org/abs/2507.15999

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