List questions from examples-counterexamples

Published on 27 May 2019 - 13:33

239

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Quotient ring of the zero-divisor ideal is a flat module

Published on 25 Mar 2026 - 11:12

129

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Differentiability class: Example of maps that are $C^k$ but not $C^{k+1}$.

Published on 28 May 2019 - 6:45

204

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Is the interior of a Jordan curve a Borel set?

Published on 25 Mar 2026 - 17:19

70

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Is there is group which can not be made into ring with any operation?

Published on 28 May 2019 - 12:34

83

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Concrete example of Lie algebra $\mathfrak{g}$ with $x$ s.t. $x$ is in the radical of $\mathfrak{g}$ but not the radical of the Killing form?

Published on 28 May 2019 - 13:05

39

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Example of fixed point free of order 2 which is not inverse mapping

Published on 28 May 2019 - 20:30

148

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Is the convex hull of a countable set a Borel set?

Published on 25 Mar 2026 - 13:59

57

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Operator with given spectrum which is not projector.

Published on 26 Mar 2026 - 3:18

405

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Topological spaces which are not pseudometrizable.

Published on 30 May 2019 - 12:23

478

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Counterexample to $g \circ f$ one-to-one $\implies$ $g$, $f$ one-to-one

Published on 26 Mar 2026 - 4:53

129

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Is the unit object in a closed monoidal category always integral?

Published on 31 May 2019 - 14:45

176

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Convergence to standard normal distribution but law of large numbers does not hold. Difficult example

Published on 27 Mar 2026 - 8:16

35

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What are some examples of statement-reason format for ratios of segments?

Published on 25 Mar 2026 - 20:13

730

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Does every linear injective open map between Banach spaces map closed sets to closed sets?

Published on 25 Mar 2026 - 22:09

List Question

Non Markov chain process.

Quotient ring of the zero-divisor ideal is a flat module

Differentiability class: Example of maps that are $C^k$ but not $C^{k+1}$.

Is the interior of a Jordan curve a Borel set?

Is there is group which can not be made into ring with any operation?

Concrete example of Lie algebra $\mathfrak{g}$ with $x$ s.t. $x$ is in the radical of $\mathfrak{g}$ but not the radical of the Killing form?

Example of fixed point free of order 2 which is not inverse mapping

Is the convex hull of a countable set a Borel set?

Operator with given spectrum which is not projector.

Topological spaces which are not pseudometrizable.

Counterexample to $g \circ f$ one-to-one $\implies$ $g$, $f$ one-to-one

Is the unit object in a closed monoidal category always integral?

Convergence to standard normal distribution but law of large numbers does not hold. Difficult example

What are some examples of statement-reason format for ratios of segments?

Does every linear injective open map between Banach spaces map closed sets to closed sets?

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