List questions from examples-counterexamples

Published on 11 Apr 2026 - 3:59

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Find a locally compact space $X$ with a subspace $A$ that is NOT locally compact.

Published on 14 Apr 2026 - 1:21

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Is there a regular not completely regular space which is not a corkscrew?

Published on 12 Apr 2026 - 15:14

109

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Hermitian matrices and their eigenvalues

Published on 14 Apr 2026 - 11:24

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Examples of mathematical results discovered "late"

Published on 12 Apr 2026 - 4:39

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For all square matrices $A$ and $B$ of the same size, it is true that $(A+B)^2 = A^2 + 2AB + B^2$?

Published on 17 Apr 2026 - 10:34

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Cartesian Product of Linearly ordered space and an example

Published on 13 Apr 2026 - 23:25

642

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Let $A\subset X$; let $f:A\to Y$ be continuous; let $Y$ be Hausdorff. Is there an example where there is no continuous function for $g$?

Published on 14 Apr 2026 - 7:08

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3x3 matrices examples to meet properties

Published on 13 Apr 2026 - 4:47

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Projection onto a subset in norm space

Published on 10 Apr 2026 - 11:59

22

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If $b+(a)$ is not a zero divisor in $R/(a)$, does it follow that $(a,b)=R$

Published on 14 Apr 2026 - 19:13

684

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Example of $f,g: [0,1]\to[0,1]$ and Riemann-integrable, but $g\circ f$ is not?

Published on 16 Apr 2026 - 3:20

437

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Intuition and counterexamples for higher-order derivative test

Published on 14 Apr 2026 - 11:13

963

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An example of an ordered, uncountable set in $\Bbb R$?

Published on 11 Apr 2026 - 14:44

656

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Decomposing real line as a union of a nullset and a set of first category

Published on 17 Apr 2026 - 6:13

List Question

Example of derivative function with limit

Find a locally compact space $X$ with a subspace $A$ that is NOT locally compact.

Is there a regular not completely regular space which is not a corkscrew?

Hermitian matrices and their eigenvalues

Examples of mathematical results discovered "late"

For all square matrices $A$ and $B$ of the same size, it is true that $(A+B)^2 = A^2 + 2AB + B^2$?

Cartesian Product of Linearly ordered space and an example

Let $A\subset X$; let $f:A\to Y$ be continuous; let $Y$ be Hausdorff. Is there an example where there is no continuous function for $g$?

3x3 matrices examples to meet properties

Projection onto a subset in norm space

If $b+(a)$ is not a zero divisor in $R/(a)$, does it follow that $(a,b)=R$

Example of $f,g: [0,1]\to[0,1]$ and Riemann-integrable, but $g\circ f$ is not?

Intuition and counterexamples for higher-order derivative test

An example of an ordered, uncountable set in $\Bbb R$?

Decomposing real line as a union of a nullset and a set of first category

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