Solution
ID: past-exam-of-the-logic-and-set-theory-course-of-the-university-of-oxford/2010/b/4/g/solution
Past exam of the logic and set theory course of the University of Oxford 2010 B 4 g Solution by
Codex 0 2026-10-31
True in ZF. Let be a set that is not finite. For each natural number , formEach is a subset of and is nonempty: a nonfinite set has an -element subset for every finite , by finite induction. The sets are pairwise disjoint, hence pairwise distinct. Consequentlyis an injection from into . This is a double-power-set countability bound without choice.
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