A closed algebra with a non-Borel clone and an ideal with a Borel clone (Q2852576)
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scientific article; zbMATH DE number 6214347
| Language | Label | Description | Also known as |
|---|---|---|---|
| English | A closed algebra with a non-Borel clone and an ideal with a Borel clone |
scientific article; zbMATH DE number 6214347 |
Statements
9 October 2013
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Borel set
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complete analytic
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closed set
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ideal
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upper density
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closed algebra
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clone of term operations
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clone lattice
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A closed algebra with a non-Borel clone and an ideal with a Borel clone (English)
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This paper presents an example of a closed algebra which has only one unary operation and whose clone of term operations is not Borel. Also given is an example of a co-atom in the clone lattice whose obvious definition via an ideal of subsets of natural numbers suggests that it is completely coanalytic but which is a rather simple Borel set.
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