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A Čech function in ZFC. (English) Zbl 1118.54002

Combining earlier results, the authors construct in ZFC a Čech function on \(\omega\), i.e. a nontrivial surjective closure operator \(\varphi:{\mathcal P}(\omega)\to{\mathcal P}(\omega)\).

MSC:

54A05 Topological spaces and generalizations (closure spaces, etc.)
54G20 Counterexamples in general topology
03E05 Other combinatorial set theory
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