English

Fundamental groups of reduced suspensions are locally free

Algebraic Topology 2026-01-13 v2

Abstract

In this paper, we analyze the fundamental group π1(ΣX,x0)\pi_1(\Sigma X,\overline{x_0}) of the reduced suspension ΣX\Sigma X where (X,x0)(X,x_0) is an arbitrary based Hausdorff space. We show that π1(ΣX,x0)\pi_1(\Sigma X,\overline{x_0}) is canonically isomorphic to a direct limit limAPπ1(ΣA,x0)\varinjlim_{A\in\mathscr{P}}\pi_1(\Sigma A,\overline{x_0}) where each group π1(ΣA,x0)\pi_1(\Sigma A,\overline{x_0}) is isomorphic to a finitely generated free group or the infinite earring group. A direct consequence of this characterization is that π1(ΣX,x0)\pi_1(\Sigma X,\overline{x_0}) is locally free for any Hausdorff space XX. Additionally, we show that ΣX\Sigma X is simply connected if and only if XX is sequentially 00-connected at x0x_0.

Keywords

Cite

@article{arxiv.2211.10499,
  title  = {Fundamental groups of reduced suspensions are locally free},
  author = {Jeremy Brazas and Patrick Gillespie},
  journal= {arXiv preprint arXiv:2211.10499},
  year   = {2026}
}

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15 pages