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example of a space that is not semilocally simply connected
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(Example)
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An example of a space that is not semilocally simply connected is the following: Let $$HR=\bigcup_{n\in\BN}\left\{(x,y)\in \BR^2\,\bigg\vert\,\left(x-\frac{1}{2^n}\right)^2+y^2= \left(\frac{1}{2^n}\right)^2\right\}$$ endowed with the subspace topology. Then $(0,0)$ has no simply connected neighborhood. Indeed every neighborhood of $(0,0)$ contains (ever diminshing) homotopically
non-trivial loops. Furthermore these loops are homotopically non-trivial even when considered as loops in $HR$ .
Figure: The Hawaiian rings
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It is essential in this example that $HR$ is endowed with the topology induced by its inclusion in the plane. In contrast, the same set endowed with the CW topology is just a bouquet of countably many circles and (as any CW complex) it is semilocaly simply connected.
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"example of a space that is not semilocally simply connected" is owned by mathcam. [ full author list (2) | owner history (1) ]
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Hawaiian rings, Hawaiian earrings |
This object's parent.
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Cross-references: CW complex, circles, plane, inclusion, induced, topology, even, loops, contains, neighborhood, simply connected, subspace topology, semilocally simply connected
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This is version 13 of example of a space that is not semilocally simply connected, born on 2003-02-04, modified 2006-06-06.
Object id is 3967, canonical name is ExampleOfASpaceThatIsNotSemilocallySimplyConnected.
Accessed 4819 times total.
Classification:
| AMS MSC: | 54D05 (General topology :: Fairly general properties :: Connected and locally connected spaces ) | | | 57M10 (Manifolds and cell complexes :: Low-dimensional topology :: Covering spaces) |
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Pending Errata and Addenda
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