English

The Topological Fundamental Group and Hoop Earring Spaces

Algebraic Topology 2010-07-09 v2 Geometric Topology

Abstract

The topological fundamental group π1top\pi_{1}^{top} is a topological invariant that assigns to each space a quasi-topological group and is discrete on spaces which are well behaved locally. For a totally path-disconnected, Hausdorff, unbased space XX, we compute the topological fundamental group of the "hoop earring" space of XX, which is the reduced suspension of XX with disjoint basepoint. We do so by factorizing the quotient map Ω(ΣX+,x)π1top(ΣX+,x)\Omega(\Sigma X_{+},x)\to \pi_{1}^{top}(\Sigma X_{+},x) through a free topological monoid with involution M(X)M(X) such that the map M(X)\shortrightarrowπ1top(ΣX+,x)M(X)\shortrightarrow \pi_{1}^{top}(\Sigma X_{+},x) is also a quotient map. π1top(ΣX+,x)\pi_{1}^{top}(\Sigma X_{+},x) is T1 and an embedding X\shortrightarrowπ1top(ΣX+,x)X\shortrightarrow \pi_{1}^{top}(\Sigma X_{+},x) illustrates that π1top(ΣX+,x)\pi_{1}^{top}(\Sigma X_{+},x) is not a topological group when XX is not regular. These hoop earring spaces provide a simple class of counterexamples to the claim that π1top\pi_{1}^{top} is a functor to the category of topological groups.

Keywords

Cite

@article{arxiv.0910.3685,
  title  = {The Topological Fundamental Group and Hoop Earring Spaces},
  author = {Jeremy Brazas},
  journal= {arXiv preprint arXiv:0910.3685},
  year   = {2010}
}

Comments

9 pages This paper has been withdrawn by the author due to much more general results appearing in the paper "The topological fundamental group and free topological groups" which includes the results in this paper. This paper, includes a sketch of the main proof (citing a thesis in progress) whereas a full proof is given in the mentioned paper.