Question

What is the Turing degree of the set of True formula of Arithmetic whose order is an infinite ordinal

score 92 · Answer 1 · 2026-02-28 03:01:21

92

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What is the Turing degree of the set of True formula of Arithmetic whose order is an infinite ordinal

Published on 28 Feb 2026 - 3:01

score 98 · Answer 2 · 2026-03-26 10:58:14

98

Views

Ordinals and initial segments

Published on 26 Mar 2026 - 10:58

score 108 · Answer 3 · 2020-05-01 17:54:44

108

Views

Prove there's no partition of $\omega_1\times \omega_1$ with the following property

Published on 01 May 2020 - 17:54

score 64 · Answer 4 · 2026-03-26 10:58:09

64

Views

Ordinal addition not commutative mistake

Published on 26 Mar 2026 - 10:58

score 88 · Answer 5 · 2020-05-02 00:18:26

88

Views

For $A\subseteq\mathbb{R}$ uncountable, prove there's no such partition of $A\times A$.

Published on 02 May 2020 - 0:18

score 93 · Answer 6 · 2020-05-03 09:52:35

93

Views

Is there a set in ZFC that can not be obtained from Ordinals

Published on 03 May 2020 - 9:52

score 102 · Answer 7 · 2020-05-05 08:02:13

102

Views

Show that if $A$ is a non-empty subset of $\omega$ such that $\bigcup A = A$, then $A=\omega$

Published on 05 May 2020 - 8:02

score 128 · Answer 8 · 2026-03-27 23:35:53

128

Views

Turing degrees of subsets of Kleene $\mathcal{O}$ which are ordinal notations of subsets of the set of recursive ordinals

Published on 27 Mar 2026 - 23:35

score 183 · Answer 9 · 2020-05-10 15:40:28

183

Views

Is this a proper recursive ordinal notation for ordinals < $\omega^2$?

Published on 10 May 2020 - 15:40

score 176 · Answer 10 · 2020-05-11 05:57:45

176

Views

About $\varepsilon_0^2 = \varepsilon_1$

Published on 11 May 2020 - 5:57

score 56 · Answer 11 · 2020-05-17 20:01:34

56

Views

Function from $\omega_1$ to $\omega$: $\exists n\in\omega~(\cup f^{-1}(n)=\omega_1)$

Published on 17 May 2020 - 20:01

score 194 · Answer 12 · 2020-05-18 23:33:18

194

Views

Strictly increasing sequence of ordinals indexed by a regular cardinal: $\text{cf}(\bigcup\{\alpha_i:i\in\kappa\})=\kappa.$

Published on 18 May 2020 - 23:33

score 88 · Answer 13 · 2020-05-23 05:48:40

88

Views

Cardinality restrictions: Too many to be included in a set

Published on 23 May 2020 - 5:48

score 141 · Answer 14 · 2020-05-24 13:25:15

141

Views

Justification of restricting to functions with finite support in the definition of ordinal exponentiation

Published on 24 May 2020 - 13:25

score 136 · Answer 15 · 2020-05-26 00:14:03

136

Views

$\sup\{\omega,\omega_\omega,\omega_{\omega_\omega},...\}=\text{?}$

Published on 26 May 2020 - 0:14

List Question

What is the Turing degree of the set of True formula of Arithmetic whose order is an infinite ordinal

Ordinals and initial segments

Prove there's no partition of $\omega_1\times \omega_1$ with the following property

Ordinal addition not commutative mistake

For $A\subseteq\mathbb{R}$ uncountable, prove there's no such partition of $A\times A$.

Is there a set in ZFC that can not be obtained from Ordinals

Show that if $A$ is a non-empty subset of $\omega$ such that $\bigcup A = A$, then $A=\omega$

Turing degrees of subsets of Kleene $\mathcal{O}$ which are ordinal notations of subsets of the set of recursive ordinals

Is this a proper recursive ordinal notation for ordinals < $\omega^2$?

About $\varepsilon_0^2 = \varepsilon_1$

Function from $\omega_1$ to $\omega$: $\exists n\in\omega~(\cup f^{-1}(n)=\omega_1)$

Strictly increasing sequence of ordinals indexed by a regular cardinal: $\text{cf}(\bigcup\{\alpha_i:i\in\kappa\})=\kappa.$

Cardinality restrictions: Too many to be included in a set

Justification of restricting to functions with finite support in the definition of ordinal exponentiation

$\sup\{\omega,\omega_\omega,\omega_{\omega_\omega},...\}=\text{?}$

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