The Topological Fundamental Group and Hoop Earring Spaces

Abstract

The topological fundamental group $π_{1}^{top}$ 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 $X$, we compute the topological fundamental group of the "hoop earring" space of $X$, which is the reduced suspension of $X$ with disjoint basepoint. We do so by factorizing the quotient map $Ω(ΣX_{+},x)\to π_{1}^{top}(ΣX_{+},x)$ through a free topological monoid with involution $M(X)$ such that the map $M(X)\shortrightarrow π_{1}^{top}(ΣX_{+},x)$ is also a quotient map. $π_{1}^{top}(ΣX_{+},x)$ is T1 and an embedding $X\shortrightarrow π_{1}^{top}(ΣX_{+},x)$ illustrates that $π_{1}^{top}(ΣX_{+},x)$ is not a topological group when $X$ is not regular. These hoop earring spaces provide a simple class of counterexamples to the claim that $π_{1}^{top}$ is a functor to the category of topological groups.