Question

How early do the second-order definable subsets of $\mathbb{N}$ occur in the Constructible Universe?

score 281 · Answer 1 · 2026-04-17 09:15:29

281

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How early do the second-order definable subsets of $\mathbb{N}$ occur in the Constructible Universe?

Published on 17 Apr 2026 - 9:15

score 76 · Answer 2 · 2026-04-13 22:35:50

76

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What is the consistency strength of $ZC+\neg CH\ \forall x (|x|>1)$?

Published on 13 Apr 2026 - 22:35

score 327 · Answer 3 · 2026-04-16 05:31:21

327

Views

If $X$ is infinite, then there is no surjective map $f : X \rightarrow WO(X)$

Published on 16 Apr 2026 - 5:31

score 78 · Answer 4 · 2026-04-10 16:43:35

78

Views

Comparing the size of ordinals involving sums of $\omega$

Published on 10 Apr 2026 - 16:43

score 99 · Answer 5 · 2026-04-14 23:21:13

99

Views

Classifying the chains of orderable sets' power sets up to isomorphism

Published on 14 Apr 2026 - 23:21

score 191 · Answer 6 · 2026-04-14 15:11:51

191

Views

$\aleph_0\times 2^{\aleph_0} = 2^{\aleph_0}$ requires the Axiom of Choice?

Published on 14 Apr 2026 - 15:11

score 190 · Answer 7 · 2026-04-14 08:00:10

190

Views

Cardinality of all infinite subsets with an infinite complement.

Published on 14 Apr 2026 - 8:00

score 294 · Answer 8 · 2026-04-14 05:31:51

294

Views

Cardinality of the set of all total orders on $\Bbb{N}$

Published on 14 Apr 2026 - 5:31

score 86 · Answer 9 · 2026-04-13 11:51:05

86

Views

Is Isles' theorem 2.6 correct?

Published on 13 Apr 2026 - 11:51

score 99 · Answer 10 · 2026-04-10 05:55:17

99

Views

Developing new theories by transfinitely iterating the Godel sentence construction

Published on 10 Apr 2026 - 5:55

score 58 · Answer 11 · 2026-04-12 00:21:08

58

Views

"Normality" condition on an ordinal operator.

Published on 12 Apr 2026 - 0:21

score 70 · Answer 12 · 2026-04-12 04:36:00

70

Views

Adding a new unary function to Morse–Kelley set theory

Published on 12 Apr 2026 - 4:36

score 70 · Answer 13 · 2026-04-16 17:58:37

Let $α$ be an ordinal and let $n\in\omega$. If $α\geq ω$ and $γ<\log (α)$, then $\log(\alpha +(\omega^{\gamma}\cdot n))=\log(\alpha)$

score 405 · Answer 14 · 2026-04-09 14:44:23

How do the consequences of Russell's paradox extend beyond universal comprehension principle as far as the set of all sets problem?

score 101 · Answer 15 · 2026-04-15 21:47:57

101

Views

Ordinals which satisfy $\beta \cdot \alpha=\alpha$

Published on 15 Apr 2026 - 21:47

List Question

How early do the second-order definable subsets of $\mathbb{N}$ occur in the Constructible Universe?

What is the consistency strength of $ZC+\neg CH\ \forall x (|x|>1)$?

If $X$ is infinite, then there is no surjective map $f : X \rightarrow WO(X)$

Comparing the size of ordinals involving sums of $\omega$

Classifying the chains of orderable sets' power sets up to isomorphism

$\aleph_0\times 2^{\aleph_0} = 2^{\aleph_0}$ requires the Axiom of Choice?

Cardinality of all infinite subsets with an infinite complement.

Cardinality of the set of all total orders on $\Bbb{N}$

Is Isles' theorem 2.6 correct?

Developing new theories by transfinitely iterating the Godel sentence construction

"Normality" condition on an ordinal operator.

Adding a new unary function to Morse–Kelley set theory

Let $α$ be an ordinal and let $n\in\omega$. If $α\geq ω$ and $γ<\log (α)$, then $\log(\alpha +(\omega^{\gamma}\cdot n))=\log(\alpha)$

How do the consequences of Russell's paradox extend beyond universal comprehension principle as far as the set of all sets problem?

Ordinals which satisfy $\beta \cdot \alpha=\alpha$

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