Question

Are there nonstandard $\mathsf{PA}$ models without $\Delta^1_1$ cuts?

score 164 · Answer 1 · 2026-03-25 15:47:08

164

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Are there nonstandard $\mathsf{PA}$ models without $\Delta^1_1$ cuts?

Published on 25 Mar 2026 - 15:47

score 153 · Answer 2 · 2026-04-08 19:52:20

153

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What is the Turing degree of truth in the second-order theory of real numbers?

Published on 08 Apr 2026 - 19:52

score 283 · Answer 3 · 2026-03-30 07:07:53

283

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A tame(ish) fragment of second-order logic

Published on 30 Mar 2026 - 7:07

score 83 · Answer 4 · 2026-04-02 16:32:20

83

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What's the purpose of the word $w$ in the proof for $ L \in \mathsf{REG} \implies L(\varphi) \in \mathsf{MSO}$ with $L(\varphi) = L$?

Published on 02 Apr 2026 - 16:32

score 83 · Answer 5 · 2021-03-24 04:48:41

83

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Candidate "AEC-yielding" fragments of bad logics

Published on 24 Mar 2021 - 4:48

score 248 · Answer 6 · 2026-03-29 14:25:09

248

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Formal or informal definability of the standard model of natural numbers

Published on 29 Mar 2026 - 14:25

score 33 · Answer 7 · 2026-04-03 16:13:59

33

Views

Writing $\forall q\, (\forall p\,q)$ instead of the schematic $\forall p\,\phi$

Published on 03 Apr 2026 - 16:13

score 72 · Answer 8 · 2026-04-09 21:08:29

72

Views

Does adding new sorts to propositional logic with quantification keep the logic second-order?

Published on 09 Apr 2026 - 21:08

score 62 · Answer 9 · 2026-04-03 17:59:55

Classical $\mathcal{A}$ quantifier: prove that $(\mathcal{A} \forall)_{1}$ relations and $\Sigma_1^1$ relations have the same expressive strength..

score 98 · Answer 10 · 2026-03-29 14:57:48

98

Views

Suggestions for learning natural deductions in simple and ramified second order logic

Published on 29 Mar 2026 - 14:57

score 229 · Answer 11 · 2021-06-04 14:30:04

229

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Expressing "finitely many", "infinitely many", "most" and "more" in second-order logic

Published on 04 Jun 2021 - 14:30

score 58 · Answer 12 · 2021-06-10 02:01:53

Can we get something equivalent to $\mathsf{ZFC2}$ by naively allowing the separation and replacement to range over second-order wffs?

score 36 · Answer 13 · 2021-06-11 16:07:58

36

Views

Prove that the prime numbers set can be defined in a model

Published on 11 Jun 2021 - 16:07

score 63 · Answer 14 · 2021-06-16 19:50:39

63

Views

Show that V is a strong limit in second-order terms

Published on 16 Jun 2021 - 19:50

score 124 · Answer 15 · 2026-03-27 02:34:22

124

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Converting a sentence to a formula in second order logic and typed first-order logic

Published on 27 Mar 2026 - 2:34

List Question

Are there nonstandard $\mathsf{PA}$ models without $\Delta^1_1$ cuts?

What is the Turing degree of truth in the second-order theory of real numbers?

A tame(ish) fragment of second-order logic

What's the purpose of the word $w$ in the proof for $ L \in \mathsf{REG} \implies L(\varphi) \in \mathsf{MSO}$ with $L(\varphi) = L$?

Candidate "AEC-yielding" fragments of bad logics

Formal or informal definability of the standard model of natural numbers

Writing $\forall q\, (\forall p\,q)$ instead of the schematic $\forall p\,\phi$

Does adding new sorts to propositional logic with quantification keep the logic second-order?

Classical $\mathcal{A}$ quantifier: prove that $(\mathcal{A} \forall)_{1}$ relations and $\Sigma_1^1$ relations have the same expressive strength..

Suggestions for learning natural deductions in simple and ramified second order logic

Expressing "finitely many", "infinitely many", "most" and "more" in second-order logic

Can we get something equivalent to $\mathsf{ZFC2}$ by naively allowing the separation and replacement to range over second-order wffs?

Prove that the prime numbers set can be defined in a model

Show that V is a strong limit in second-order terms

Converting a sentence to a formula in second order logic and typed first-order logic

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