List questions from examples-counterexamples

Published on 13 Jun 2019 - 9:12

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Questioning dense subset completeness (counterexample)

Published on 26 Mar 2026 - 6:18

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If $f$ is absolutely continuous $\sqrt(f)$ may not be

Published on 23 Feb 2026 - 4:55

102

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Set theory based on different logic

Published on 13 Jun 2019 - 16:26

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find 2×2 matrix such that $ A^2 =-I$

Published on 14 Jun 2019 - 15:30

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Counterexample to $ \frac{\mathrm{d}{y}}{\mathrm{d}{x}} = \frac{1}{\left( \frac{\mathrm{d}{x}}{\mathrm{d}{y}} \right)} $

Published on 15 Jun 2019 - 13:00

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Hard inequality :$\sum_{cyc}\frac{a}{\sqrt[3]{a+b}}\leq a+b^{\frac{2}{3}}+c$

Published on 15 Jun 2019 - 14:24

260

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Counter example for Baire's Theorem

Published on 29 Mar 2026 - 3:02

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Defining Multiplication on Strongly Homogeneous Commutative Semigroups

Published on 25 Mar 2026 - 7:40

85

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Compositeness test for numbers of the form $E_n(b)=\frac{b^{2^n}+1}{2}$

Published on 17 Jun 2019 - 17:36

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Do these functions exist?

Published on 18 Jun 2019 - 3:18

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Can this set-theoretic vector space be endowed with this operation so that everything is fine?

Published on 18 Jun 2019 - 8:14

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Counterexample to the primality test

Published on 26 Mar 2026 - 6:03

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Suppose that $f: \mathbb R^n \to \mathbb R^n$ is a bijection and $n\geq2$. Can $f$ send every open set onto non-open set?

Published on 18 Jun 2019 - 16:14

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Eigenvalue and similar matrices

Published on 19 Jun 2019 - 5:15

List Question

Connection between composition and "inner composition" in closed monoidal categories

Questioning dense subset completeness (counterexample)

If $f$ is absolutely continuous $\sqrt(f)$ may not be

Set theory based on different logic

find 2×2 matrix such that $ A^2 =-I$

Counterexample to $ \frac{\mathrm{d}{y}}{\mathrm{d}{x}} = \frac{1}{\left( \frac{\mathrm{d}{x}}{\mathrm{d}{y}} \right)} $

Hard inequality :$\sum_{cyc}\frac{a}{\sqrt[3]{a+b}}\leq a+b^{\frac{2}{3}}+c$

Counter example for Baire's Theorem

Defining Multiplication on Strongly Homogeneous Commutative Semigroups

Compositeness test for numbers of the form $E_n(b)=\frac{b^{2^n}+1}{2}$

Do these functions exist?

Can this set-theoretic vector space be endowed with this operation so that everything is fine?

Counterexample to the primality test

Suppose that $f: \mathbb R^n \to \mathbb R^n$ is a bijection and $n\geq2$. Can $f$ send every open set onto non-open set?

Eigenvalue and similar matrices

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