List questions from examples-counterexamples

Published on 05 Apr 2018 - 17:48

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Legendre polynomials and primality testing

Published on 25 Mar 2026 - 6:23

131

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If $x \in \overline{A}$ implies $x$ is the limit of a sequence in $A$ for all $A \subset X$, is $X$ first-countable?

Published on 06 Apr 2018 - 22:52

63

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is there a harmonic function such that ${\partial f \over \partial r}$ isn't harmonic?

Published on 25 Mar 2026 - 6:01

96

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When do integrals converge, but absolute values of integrals not converge?

Published on 25 Mar 2026 - 12:53

58

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Example of curve in $R^2$ which kills driver affirmation

Published on 25 Mar 2026 - 3:01

370

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A congruence involving Fibonacci polynomials

Published on 25 Mar 2026 - 12:36

43

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$ A \subset \Bbb R$ is bounded and not compact, exhibit $f: A \to \Bbb R$ that isn't bounded

Published on 10 Apr 2018 - 16:29

162

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Elementary examples of pointwise sequential closures that are not pointwise closed

Published on 10 Apr 2018 - 16:37

534

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Counter-example for the Slutsky Theorem

Published on 11 Apr 2018 - 13:45

54

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Proofs by counter example

Published on 25 Mar 2026 - 15:56

44

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Does there exist a natural number $N = xy$ satisfying $D(x)D(y) = 2s(x)s(y)$ with $\gcd(x,y)=1$?

Published on 25 Mar 2026 - 14:54

46

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Does there exist an odd natural number $N = xy$ satisfying $D(x)D(y) = 2s(x)s(y)$?

Published on 25 Mar 2026 - 1:18

229

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Replacing Predicates in First Order Statements to Produce a Counter-Example World

Published on 13 Apr 2018 - 6:23

153

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A counterexample to the Sura-Bura Theorem for non separated compact spaces

Published on 14 Apr 2018 - 20:22

List Question

Example of normal subgroup that contains the commutator group as a proper subgroup.

Legendre polynomials and primality testing

If $x \in \overline{A}$ implies $x$ is the limit of a sequence in $A$ for all $A \subset X$, is $X$ first-countable?

is there a harmonic function such that ${\partial f \over \partial r}$ isn't harmonic?

When do integrals converge, but absolute values of integrals not converge?

Example of curve in $R^2$ which kills driver affirmation

A congruence involving Fibonacci polynomials

$ A \subset \Bbb R$ is bounded and not compact, exhibit $f: A \to \Bbb R$ that isn't bounded

Elementary examples of pointwise sequential closures that are not pointwise closed

Counter-example for the Slutsky Theorem

Proofs by counter example

Does there exist a natural number $N = xy$ satisfying $D(x)D(y) = 2s(x)s(y)$ with $\gcd(x,y)=1$?

Does there exist an odd natural number $N = xy$ satisfying $D(x)D(y) = 2s(x)s(y)$?

Replacing Predicates in First Order Statements to Produce a Counter-Example World

A counterexample to the Sura-Bura Theorem for non separated compact spaces

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