Question

Can't the first (/second) transinfinite ordinal replace the first (/second) uncountable ordinal in several counterexamples?

score 191 · Answer 1 · 2026-03-30 17:52:07

191

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Can't the first (/second) transinfinite ordinal replace the first (/second) uncountable ordinal in several counterexamples?

Published on 30 Mar 2026 - 17:52

score 2.9k · Answer 2 · 2026-03-25 17:44:47

2.9k

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First countable + separable imply second countable?

Published on 25 Mar 2026 - 17:44

score 9.8k · Answer 3 · 2026-04-01 13:44:47

9.8k

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Non-associative commutative binary operation

Published on 01 Apr 2026 - 13:44

score 69 · Answer 4 · 2026-04-01 08:08:02

69

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$f_{\scriptscriptstyle{\vert H}}=g_{\scriptscriptstyle{\vert H}}$ implies $f=g$ for groups

Published on 01 Apr 2026 - 8:08

score 771 · Answer 5 · 2026-04-12 00:56:25

771

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Finding an example of nonhomeomorphic closed connected sets

Published on 12 Apr 2026 - 0:56

score 461 · Answer 6 · 2026-04-11 17:46:52

461

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Questions on symmetric difference of events

Published on 11 Apr 2026 - 17:46

score 404 · Answer 7 · 2026-04-01 20:25:31

404

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counterexample to a "theorem" on continuity of largest deltas for continuous functions $f:[a,b]\to\mathbb{R}$

Published on 01 Apr 2026 - 20:25

score 43 · Answer 8 · 2026-03-28 15:20:06

43

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Equality of two multilinear forms

Published on 28 Mar 2026 - 15:20

score 120 · Answer 9 · 2026-04-12 02:41:41

120

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What are some interesting cases where the two obvious definitions of "discrete object" diverge?

Published on 12 Apr 2026 - 2:41

score 2.7k · Answer 10 · 2026-04-09 13:20:09

2.7k

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Limit point Compactness does not imply compactness counter-example

Published on 09 Apr 2026 - 13:20

score 8k · Answer 11 · 2026-04-10 20:04:41

8k

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Examples of bounded linear operators with range not closed

Published on 10 Apr 2026 - 20:04

score 2.4k · Answer 12 · 2016-01-28 21:52:21

2.4k

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Find a False Counterexample for : "$\forall$ $A, B$ and $C$, we have $A \cap (B - C) = (A \cap B) - (A \cap C)$"

Published on 28 Jan 2016 - 21:52

score 538 · Answer 13 · 2026-04-11 04:39:14

538

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Does anybody know an example for a matrix with nullspace property for nonnegative signals?

Published on 11 Apr 2026 - 4:39

score 108 · Answer 14 · 2016-01-29 20:57:37

108

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If $A\dot{-} B$ is countable and $B \dot{-} C$ is countable then $A\dot{-} C$ is countable?

Published on 29 Jan 2016 - 20:57

score 4.2k · Answer 15 · 2026-04-03 00:22:04

4.2k

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If $\{x_n\}$ satisfies that $x_{n+1} - x_n$ goes to $0$, is $\{x_n\}$ a Cauchy sequence?

Published on 03 Apr 2026 - 0:22

List Question

Can't the first (/second) transinfinite ordinal replace the first (/second) uncountable ordinal in several counterexamples?

First countable + separable imply second countable?

Non-associative commutative binary operation

$f_{\scriptscriptstyle{\vert H}}=g_{\scriptscriptstyle{\vert H}}$ implies $f=g$ for groups

Finding an example of nonhomeomorphic closed connected sets

Questions on symmetric difference of events

counterexample to a "theorem" on continuity of largest deltas for continuous functions $f:[a,b]\to\mathbb{R}$

Equality of two multilinear forms

What are some interesting cases where the two obvious definitions of "discrete object" diverge?

Limit point Compactness does not imply compactness counter-example

Examples of bounded linear operators with range not closed

Find a False Counterexample for : "$\forall$ $A, B$ and $C$, we have $A \cap (B - C) = (A \cap B) - (A \cap C)$"

Does anybody know an example for a matrix with nullspace property for nonnegative signals?

If $A\dot{-} B$ is countable and $B \dot{-} C$ is countable then $A\dot{-} C$ is countable?

If $\{x_n\}$ satisfies that $x_{n+1} - x_n$ goes to $0$, is $\{x_n\}$ a Cauchy sequence?

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