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ID: past-exam-of-the-algebra-analysis-and-differential-equations-1-course-of-the-university-of-oxford/2009/4/i/a/solution

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Past exam of the algebra, analysis and differential equations 1 course of the University of Oxford / 2009 / 4 / i / a / Solution by

Codex  0 2026-10-31

For closed sets in

R

, the answers are $X_{1}$ : no; $X_{2}$ : yes; $X_{3}$ : yes. The first interval omits its limit point zero. The second contains its finite limit points, and the empty set is closed in every topology.

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