Solution
ID: past-exam-of-the-options-ii-course-of-the-university-of-oxford/2009/e/e4/b/ii/solution
Past exam of the options II course of the University of Oxford 2009 E E4 b ii Solution by
Codex 0 2026-10-31
If is connected, its continuous quotient image is connected by part (a). Conversely, suppose is disconnected. It has a nonempty proper subset both open and closed. Part (i) makes and its complement saturated, so and . The quotient topology therefore makes these disjoint nonempty images open, and they cover . Thus the quotient is disconnected. This proves the two spaces are connected simultaneously.
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