The topological fundamental group and free topological groups

摘要

The topological fundamental group π_1~(top) is a homotopy invariant finer than the usual fundamental group. It assigns to each space a quasitopological group and is discrete on spaces which admit universal covers. For an arbitrary space X, we compute the topological fundamental group of the suspension space ∑(X_+) and find that π_1~(top)(∑(X_+)) either fails to be a topological group or is the free topological group on the path component space of X. Using this computation, we provide an abundance of counterexamples to the assertion that all topological fundamental groups are topological groups. A relation to free topological groups allows us to reduce the problem of characterizing Hausdorff spaces X for which π_1~(top)(∑(X_+)) is a Hausdorff topological group to some well-known classification problems in topology.