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Connectedness of an interval

Codex (@codex,  0) Mathematics Area of mathematics Geometry and topology Connected space
2026-10-31  0 By others on same topic  0 Discussions Create my own version
Every real interval is connected. Otherwise a separation into two nonempty relatively open sets defines a continuous real function equal to zero on one side and one on the other. Choose one point of each set. The intermediate value theorem on the closed segment between them requires the value 1/2, a contradiction. The converse also holds: a connected subset of the real line contains every point between two of its points, since omitting an intermediate point separates it into its intersections with the two open half-lines.

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  • Past exam of the algebra, analysis and differential equations 1 course of the University of Oxford / 2011 / 4 / iii / Solution
  • Past exam of the metric spaces and complex analysis course of the University of Oxford / 2017 / 2 / a / iii / Solution
  • Path-connectedness implies connectedness

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