List questions from examples-counterexamples

Published on 26 Mar 2026 - 1:01

130

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Is the function $f(x,y)=y \cdot \text{sign}(x)$ Sobolev?

Published on 25 Mar 2026 - 11:19

299

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Example of $\lim\inf x_n+\lim \inf y_n<\lim \inf(x_n+y_n)$

Published on 26 Mar 2026 - 1:25

100

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Example for a covering map with not equal groups from different base points

Published on 25 Mar 2026 - 20:41

175

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Counterexample of discontinuous function for integration by parts

Published on 07 Nov 2018 - 6:29

631

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Negative Curvature on Torus

Published on 25 Mar 2026 - 17:36

435

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A measure for which Lusin's theorem fails?

Published on 25 Mar 2026 - 3:00

134

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formulas such that either "$\mathcal{M} \vDash \phi$, then $\mathcal{M} \vDash \psi$" or "$\mathcal{M} \vDash \phi \rightarrow \psi$"

Published on 26 Mar 2026 - 21:53

376

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A topological space with the Universal Extension Property which is not homeomorphic to a retract of $\mathbb{R}^J$?

Published on 23 Feb 2026 - 3:00

322

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For what spaces does every countable Borel cover have a finite subcover?

Published on 25 Mar 2026 - 9:12

315

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Probable prime tests for generalized repunit numbers

Published on 26 Mar 2026 - 1:34

174

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$(X,T)$ is compact iff every family of closed set ${F}_{i \in I}$ with non-empty finite intersections has an overall intersection that is not empty.

Published on 09 Nov 2018 - 14:02

182

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Inequality involving convolutions

Published on 26 Mar 2026 - 9:49

394

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A dense measure $0$ $G_\delta$ subset of the Fat Cantor set?

Published on 25 Mar 2026 - 9:18

1k

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Give an example of a real valued function on $[0,1]$ satisfying the following property.

Published on 12 Nov 2018 - 18:17

List Question

Open connected subsets of path connected spaces

Is the function $f(x,y)=y \cdot \text{sign}(x)$ Sobolev?

Example of $\lim\inf x_n+\lim \inf y_n<\lim \inf(x_n+y_n)$

Example for a covering map with not equal groups from different base points

Counterexample of discontinuous function for integration by parts

Negative Curvature on Torus

A measure for which Lusin's theorem fails?

formulas such that either "$\mathcal{M} \vDash \phi$, then $\mathcal{M} \vDash \psi$" or "$\mathcal{M} \vDash \phi \rightarrow \psi$"

A topological space with the Universal Extension Property which is not homeomorphic to a retract of $\mathbb{R}^J$?

For what spaces does every countable Borel cover have a finite subcover?

Probable prime tests for generalized repunit numbers

$(X,T)$ is compact iff every family of closed set ${F}_{i \in I}$ with non-empty finite intersections has an overall intersection that is not empty.

Inequality involving convolutions

A dense measure $0$ $G_\delta$ subset of the Fat Cantor set?

Give an example of a real valued function on $[0,1]$ satisfying the following property.

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