List questions from descriptive-set-theory

Published on 29 Apr 2026 - 12:55

959

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Cardinality of closed sets of reals

Published on 29 Apr 2026 - 12:55

182

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A set with Borel preimage

Published on 17 Apr 2026 - 2:44

141

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Existence of open set in $R^2$ such that all open sets in $R$ are contained among its vertical sections

Published on 12 Apr 2026 - 22:21

588

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Is the sum (difference) of Borel set with itself a Borel set?

Published on 05 May 2026 - 4:11

160

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Do abstract harmonic analysts use topological methods to solve problems or deal with Borel hierarchy?

Published on 29 Apr 2026 - 12:55

229

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Question on a proof of Kuratowski's Theorem in Kechris's Classical Descriptive Set Theory

Published on 29 Apr 2026 - 12:55

89

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If $f$ is continuous on $A,$ is it true that $\{x:\text{osc}_f(x)=0\}=A?$

Published on 05 May 2026 - 4:10

233

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Show that for $\xi>1,$ $A \text{ is } \Delta_{\xi+1}^0 \iff A=\lim_nA_n\text{ for some } A_n\in\Delta_\xi^0.$

Published on 29 Apr 2026 - 12:56

169

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Determinacy of complement of set

Published on 29 Apr 2026 - 12:55

4k

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Is the pre-image of a Borel set by a continuous function a Borel set? Is it an open set?

Published on 12 Apr 2026 - 5:35

78

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Extending the lim function

Published on 09 Apr 2026 - 15:23

35

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Continuous multivalued mapping on compact metric spaces

Published on 08 Apr 2026 - 21:58

899

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Can an uncountable subset of $\mathbb{R}$ have empty intersection with its derived set?

Published on 29 Apr 2026 - 12:55

313

Views

Is countable choice enough to prove that there are continuum-many Borel sets?

Published on 11 Apr 2026 - 23:13

List Question

Do derived sets have anything similar to derivatives?

Cardinality of closed sets of reals

A set with Borel preimage

Existence of open set in $R^2$ such that all open sets in $R$ are contained among its vertical sections

Is the sum (difference) of Borel set with itself a Borel set?

Do abstract harmonic analysts use topological methods to solve problems or deal with Borel hierarchy?

Question on a proof of Kuratowski's Theorem in Kechris's Classical Descriptive Set Theory

If $f$ is continuous on $A,$ is it true that $\{x:\text{osc}_f(x)=0\}=A?$

Show that for $\xi>1,$ $A \text{ is } \Delta_{\xi+1}^0 \iff A=\lim_nA_n\text{ for some } A_n\in\Delta_\xi^0.$

Determinacy of complement of set

Is the pre-image of a Borel set by a continuous function a Borel set? Is it an open set?

Extending the lim function

Continuous multivalued mapping on compact metric spaces

Can an uncountable subset of $\mathbb{R}$ have empty intersection with its derived set?

Is countable choice enough to prove that there are continuum-many Borel sets?

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