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The bookUnit 2 · Topology52 / 83

Connectedness and components

Why this is asked: Components are always closed but not always open; in ℚ every component is a single point. Use clopen sets or a continuous surjection onto {0,1} to disprove connectedness.

Connectedness, components and totally disconnected spaces

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See it move

The topologist's sine curve, walkedinteractive

Walk along sin(1/x) toward the segment and watch the distance meter diverge — connected, but no path gets there.

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The trap here

“Connected components are open” — false

Q\mathbb{Q} with the usual topology

Components are singletons, which are not open. They are open exactly when the space is locally connected.

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Open this in the full syllabus view · Unit 2