The topological fundamental group and generalized covering spaces

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The topological fundamental group $\pi_{1}^{top}$ 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 $X$, 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 $\Omega(\Sigma X_{+},x)\to \pi_{1}^{top}(\Sigma X_{+},x)$ through a free topological monoid with involution $M(X)$ such that the map $M(X)\shortrightarrow \pi_{1}^{top}(\Sigma X_{+},x)$ is also a quotient map. $\pi_{1}^{top}(\Sigma X_{+},x)$ is T1 and an embedding $X\shortrightarrow \pi_{1}^{top}(\Sigma X_{+},x)$ illustrates that $\pi_{1}^{top}(\Sigma X_{+},x)$ is not a topological group when $X$ is not regular. These hoop earring spaces provide a simple class of counterexamples to the claim that $\pi_{1}^{top}$ is a functor to the category of topological groups.




Biss, D. K. (2002). The topological fundamental group and generalized covering spaces. Topology and Its Applications, 124(3), 355–371.

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