User Noah Schweber

10 votes

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Comprehension axiom that helps in the opposite direction

answered Apr 22, 2022 at 1:30

10 votes

Consistency of $c=2^{\aleph_0}=2^{\aleph_1}=\ldots=2^{\aleph_n}\ldots$, for every $n<\omega$

answered Sep 11, 2022 at 22:09

9 votes

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Is there a proof of independence of AC from Z that is done in Z?

answered Sep 22, 2022 at 19:15

9 votes

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What is the meaning of $\alpha^{+L}$ for $\alpha$ an infinite countable ordinal?

answered Oct 21, 2022 at 17:20

9 votes

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Infinitary reasoning in Godel's Completeness Proof

answered Jul 18, 2019 at 3:04

9 votes

Is Axiom of Choice equivalent to its version for families of sets, indexed by ordinals?

answered Apr 23, 2020 at 21:39

9 votes

Accepted

Arithmetic statement which is independent, and whose independence is independent, and so on?

answered Aug 5, 2020 at 20:59

9 votes

Are there structures in a finite signature that are recursively categorically axiomatizable in SOL but not finitely categorically axiomatizable?

answered Apr 10, 2021 at 0:48

9 votes

Example of a $\Pi^2_2$ sentence?

answered Aug 17, 2021 at 23:23

9 votes

Operations on the set of large cardinal axioms

answered Oct 4, 2023 at 16:55

9 votes

Does PA prove (Artemov-style) the consistency of a stronger system?

answered Apr 17 at 6:43

9 votes

Accepted

Is it a theorem of ZF that a non-empty countable Cartesian product of finite non-singleton sets has the cardinality of the continuum?

answered Jun 5 at 23:44

9 votes

At what ordinal $\chi$ does $\mathrm{L}_\chi$ contain a surjection from $\omega$ to $\mathrm{L}_{\beta_0}$?

answered Jul 18 at 19:16

9 votes

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Negating fundamental axioms

answered Jul 7 at 19:52

9 votes

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What can be achieved by liberalizing induction for $RCA_0$?

answered Oct 5, 2015 at 21:06

9 votes

Is Turing degree actually useful in real life?

answered Feb 14, 2014 at 21:42

9 votes

"the" random permutation

answered Jun 6, 2014 at 0:56

9 votes

Ordinal Exponentiation in Genzen's Sequent Calculus

answered Aug 2, 2013 at 3:49

9 votes

Accepted

Question on Godel completeness theorem

answered Mar 26, 2013 at 17:38

9 votes

A question about Second-Order ZFC and the Continuum Hypothesis

answered Oct 13, 2011 at 23:50

9 votes

Examples of conjectures that were widely believed to be true but later proved false

answered May 4, 2012 at 15:48

9 votes

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What is the largest large-cardinal hypothesis consistent with $ZFC + V=L$?

answered Dec 9, 2016 at 2:13

9 votes

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Provably undecidable problems within prime numbers context

answered Aug 23, 2016 at 21:06

9 votes

Henkin semantics for second-order logic

answered May 1, 2016 at 23:38

9 votes

Mathematical Evidence Backing $|\mathbb{R}|=\aleph_2$

answered Jul 30, 2018 at 3:49

9 votes

Ordinal analysis and proofs of consistency

answered Jun 8, 2019 at 6:35

8 votes

Accepted

Amorphous proper classes in MK

answered Mar 19, 2019 at 21:07

8 votes

Forcing CH but not adding $\omega_1$-sequences

answered Aug 28, 2018 at 2:37

8 votes

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On the "infinitely often in" relation between subsets of $\mathbb{N}$

answered Jan 8, 2019 at 15:42

8 votes

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What is the consistency strength of non-existence of outer automorphisms of Calkin algebra?

answered Jul 28, 2018 at 20:32

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478 Answers

Comprehension axiom that helps in the opposite direction

Consistency of $c=2^{\aleph_0}=2^{\aleph_1}=\ldots=2^{\aleph_n}\ldots$, for every $n<\omega$

Is there a proof of independence of AC from Z that is done in Z?

What is the meaning of $\alpha^{+L}$ for $\alpha$ an infinite countable ordinal?

Infinitary reasoning in Godel's Completeness Proof

Is Axiom of Choice equivalent to its version for families of sets, indexed by ordinals?

Arithmetic statement which is independent, and whose independence is independent, and so on?

Are there structures in a finite signature that are recursively categorically axiomatizable in SOL but not finitely categorically axiomatizable?

Example of a $\Pi^2_2$ sentence?

Operations on the set of large cardinal axioms

Does PA prove (Artemov-style) the consistency of a stronger system?

Is it a theorem of ZF that a non-empty countable Cartesian product of finite non-singleton sets has the cardinality of the continuum?

At what ordinal $\chi$ does $\mathrm{L}_\chi$ contain a surjection from $\omega$ to $\mathrm{L}_{\beta_0}$?

Negating fundamental axioms

What can be achieved by liberalizing induction for $RCA_0$?

Is Turing degree actually useful in real life?

"the" random permutation

Ordinal Exponentiation in Genzen's Sequent Calculus

Question on Godel completeness theorem

A question about Second-Order ZFC and the Continuum Hypothesis

Examples of conjectures that were widely believed to be true but later proved false

What is the largest large-cardinal hypothesis consistent with $ZFC + V=L$?

Provably undecidable problems within prime numbers context

Henkin semantics for second-order logic

Mathematical Evidence Backing $|\mathbb{R}|=\aleph_2$

Ordinal analysis and proofs of consistency

Amorphous proper classes in MK

Forcing CH but not adding $\omega_1$-sequences

On the "infinitely often in" relation between subsets of $\mathbb{N}$

What is the consistency strength of non-existence of outer automorphisms of Calkin algebra?