List questions from examples-counterexamples

Published on 14 Apr 2026 - 6:56

84

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Nontrivial example of a discontinuous real-valued convex function?

Published on 13 Apr 2026 - 20:40

120

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For Riemann integral partitions, does it matter whether $f$ is evaluated at a point in $(t_{i-1},t_i)$ or $[t_{i-1},t_i]$?

Published on 14 Apr 2026 - 18:11

1.5k

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Proving and supplying counterexamples for few basic facts regarding open and closed sets

Published on 16 Apr 2026 - 23:22

85

Views

A vector space $V$ such that $V\otimes V \not \cong B(V^*)$

Published on 14 Apr 2026 - 15:10

245

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Visualizing lower bound for the Happy Ending Problem (small cases).

Published on 15 Apr 2026 - 7:10

389

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Simple examples of undergraduate real analysis that cannot be written in the language of first-order logic

Published on 10 Apr 2026 - 21:47

54

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Topology counter example

Published on 11 Apr 2026 - 7:49

374

Views

Sum of unbounded functions

Published on 12 Apr 2026 - 21:06

45

Views

Pre-image of sigma algebra is sigma-algebra, What is wrong with that counterexample?

Published on 14 Apr 2026 - 4:26

598

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A semigroup with only one idempotent element is not a group counterexample.

Published on 12 Apr 2026 - 0:40

171

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Non Pathological examples of non sequential spaces

Published on 14 Apr 2026 - 5:57

104

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Is there a nonrigid space X homeomorphic to X/Aut(X)?

Published on 14 Apr 2026 - 19:39

581

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Co-finite and Co-countable topologies are not normal

Published on 15 Apr 2026 - 11:29

133

Views

An other total-variation inequality of mine

Published on 11 Apr 2026 - 18:58

List Question

handshaking lemma and Erdos-Gallai theorem

Nontrivial example of a discontinuous real-valued convex function?

For Riemann integral partitions, does it matter whether $f$ is evaluated at a point in $(t_{i-1},t_i)$ or $[t_{i-1},t_i]$?

Proving and supplying counterexamples for few basic facts regarding open and closed sets

A vector space $V$ such that $V\otimes V \not \cong B(V^*)$

Visualizing lower bound for the Happy Ending Problem (small cases).

Simple examples of undergraduate real analysis that cannot be written in the language of first-order logic

Topology counter example

Sum of unbounded functions

Pre-image of sigma algebra is sigma-algebra, What is wrong with that counterexample?

A semigroup with only one idempotent element is not a group counterexample.

Non Pathological examples of non sequential spaces

Is there a nonrigid space X homeomorphic to X/Aut(X)?

Co-finite and Co-countable topologies are not normal

An other total-variation inequality of mine

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