Components and local (path) connectedness

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A topological space XX is called locally path connected at xx if for each open set VV containing xx, there is a path connected open set UU with x∈U⊂Vx \in U \subset V. It is called locally path connected if it is locally path connected at each x∈Xx \in X. It is called locally connected at xx if, for each open set VV containing xx, there is a connected open set UU with x∈U⊂Vx \in U \subset V. It is called locally connected if it is locally connected for each x∈Xx \in X.

Show that a locally path connected space is locally connected.

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Show that the topologist's sine curve (see the figure in Exercise 1.9.44) is not locally connected, where a space is locally connected at xx if for each open set VV containing xx, there is a connected open set UU with x∈U⊂Vx \in U \subset V.

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Show that an open set in Rn\mathbb {R}^{n} is locally path connected, where a space is locally path connected at xx if for each open set VV containing xx, there is a path connected open set UU with x∈U⊂Vx \in U \subset V.

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Show that the path components of a locally path connected space are open sets, where a space is locally path connected at xx if for each open set VV containing xx, there is a path connected open set UU with x∈U⊂Vx \in U \subset V.

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Show that if XX is locally path connected and connected, then XX is path connected.

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Remark.
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Modify the proof that a connected open set in Rn\mathbb {R}^{n} is path connected.

Give an example of a path connected space which is not locally path connected.

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Problem 1.9.53 from Lawson T. "Topology: A Geometric Approach" [Law06]More problems in Section 1.9 "Supplementary exercises"

Define an equivalence relation on XX by x∼yx \sim y if there is a connected set containing both xx and yy. The equivalence classes are called the components of XX.

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(a)

Verify that this is an equivalence relation.

(b)

Show that each component is connected, that any two components are equal or disjoint, and that the union of the components is XX.

(c)

Show that any connected subset of XX intersects at most one component and is a subset of that component.

(d)

Show that each path component is contained in a component, and that a component is a disjoint union of path components.

(e)

Show that a component is a closed set.

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(a)

Show that a space is locally connected iff, for each open set UU, each component of UU is open in XX.

(b)

Show that a space is locally path connected iff, for each open set UU, each path component of UU is open in XX.

Prove that if an open set U⊂R2U \subset \mathbb {R}^{2} is path connected, then any two points in UU can actually be connected by a polygonal path in UU.

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Show that a connected nn-manifold is path connected.

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Remark.
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Mimic the proof that a connected open set in Rn\mathbb {R}^{n} is path connected, or use Exercise 1.9.51.

References

[Law06] Lawson T. Topology: A Geometric Approach. Oxford University Press, 2006.