Paper 3, Section I, 3F3 F

Metric and Topological Spaces | Part IB, 2012

Define the notion of a connected component of a space XX.

If AαXA_{\alpha} \subset X are connected subsets of XX such that αAα\bigcap_{\alpha} A_{\alpha} \neq \emptyset, show that αAα\bigcup_{\alpha} A_{\alpha} is connected.

Prove that any point xXx \in X is contained in a unique connected component.

Let XRX \subset \mathbb{R} consist of the points 0,1,12,13,,1n,0,1, \frac{1}{2}, \frac{1}{3}, \ldots, \frac{1}{n}, \ldots. What are the connected components of XX ?

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