List questions from examples-counterexamples

Published on 14 Apr 2026 - 16:27

225

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Bidual of a WSC space

Published on 14 Apr 2026 - 12:00

32.7k

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Is the rank of $AB$ always equal to the rank of $BA$?

Published on 15 Apr 2026 - 6:35

739

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Example of a topological vector space such that $E = M \oplus N$ algebraically, but not topologically

Published on 16 Apr 2026 - 13:52

293

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Can someone give me a counterexample to disprove this statement?

Published on 13 Apr 2026 - 9:48

6.4k

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Does $G\cong G/H$ imply that $H$ is trivial?

Published on 11 Apr 2026 - 11:14

3.2k

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Opposite of a contraction mapping

Published on 22 Apr 2026 - 22:04

9.4k

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An example of an easy to understand undecidable problem

Published on 10 Apr 2026 - 4:56

85

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if $ax|n$ and $ax+1$ is prime does $ax+1|a^{n}-1$?

Published on 10 Apr 2026 - 16:08

2.7k

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A counterexample to theorem about orthogonal projection

Published on 10 Apr 2026 - 16:11

25.7k

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More examples of Simpson's Paradox, barring the ones on Wikipedia, Titanic, and delayed flights.

Published on 14 Apr 2026 - 23:56

1.1k

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Measure Product Theorem: may non-$\sigma$-finiteness result unique product?

Published on 11 Apr 2026 - 11:21

2.5k

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Sum of Cauchy Sequences Cauchy?

Published on 13 Apr 2026 - 6:05

1.6k

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Weird measurable set

Published on 11 Apr 2026 - 18:51

443

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If a sub-C*-algebra does not contain the unit, is it contained in a proper ideal?

Published on 11 Apr 2026 - 9:16

List Question

Give an example that $\overline{A \cap B} \neq \overline{A} \cap \overline{B}$

Bidual of a WSC space

Is the rank of $AB$ always equal to the rank of $BA$?

Example of a topological vector space such that $E = M \oplus N$ algebraically, but not topologically

Can someone give me a counterexample to disprove this statement?

Does $G\cong G/H$ imply that $H$ is trivial?

Opposite of a contraction mapping

An example of an easy to understand undecidable problem

if $ax|n$ and $ax+1$ is prime does $ax+1|a^{n}-1$?

A counterexample to theorem about orthogonal projection

More examples of Simpson's Paradox, barring the ones on Wikipedia, Titanic, and delayed flights.

Measure Product Theorem: may non-$\sigma$-finiteness result unique product?

Sum of Cauchy Sequences Cauchy?

Weird measurable set

If a sub-C*-algebra does not contain the unit, is it contained in a proper ideal?

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