Borel ideals vs. Borel sets of countable relations and trees (Q1120573)

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scientific article; zbMATH DE number 4101183
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Borel ideals vs. Borel sets of countable relations and trees
scientific article; zbMATH DE number 4101183

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    Borel ideals vs. Borel sets of countable relations and trees (English)
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    1989
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    For \(\mu\), a countable ordinal, let \(I_{\mu}\) be the ideal of subsets of \(\omega^{\mu}\) with order type less than \(\omega^{\mu}\). It is shown that, when appropriately coded, \(I_{\mu}\) is a \(\Sigma^ 0_{2\mu}\)-complete Borel set. This result is extended to partial orders representing small ordinals, trees with small ranks, etc. The proofs are based on Wadge games.
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    Borel classifications
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    ideal of subsets
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    Borel set
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    partial orders representing small ordinals
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    trees with small ranks
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    Wadge games
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