User C7X

18 votes

Accepted

Finite verification for theorems due to Busy Beaver numbers

answered Jul 14 at 23:45

7 votes

Most recent results on formulating Kunen's inconsistency theorem in ZF without choice

answered Apr 5 at 6:28

6 votes

Smallest ordinal modelling $\aleph_1$?

answered Apr 27, 2022 at 20:21

5 votes

Do all limit $\alpha \in \omega_1^L$ satisfy $L_\alpha \models V=HC$?

answered May 4, 2022 at 14:19

5 votes

Iterated Gentzen: or, a Sith objection to the proof of consistency of PA

answered Apr 16, 2022 at 5:03

5 votes

Important open problems that have already been reduced to a finite but infeasible amount of computation

answered May 17, 2023 at 20:46

5 votes

What are some noteworthy "mic-drop" moments in math?

answered Oct 26, 2023 at 11:34

5 votes

When is 2 qualitatively different from 3?

answered Nov 10 at 21:48

5 votes

When is 4 qualitatively different than $n\leq 3$?

answered Nov 11 at 3:34

4 votes

Accepted

What are the known large cardinal axioms for which weaker and stronger set theories "catch up"?

answered Sep 4 at 17:28

4 votes

Theorems with many distinct proofs

answered Apr 27 at 1:52

4 votes

How can I catalog these generalized Collatz problems?

answered Feb 25 at 0:14

3 votes

Harvey Friedman: The expanding mind

answered Apr 18 at 5:51

3 votes

End-extension in Gödel's constructible universe

answered Mar 21 at 5:12

3 votes

Is all ordinary mathematics contained in high school mathematics?

answered Jul 23, 2022 at 21:58

3 votes

Parameter-free effective cardinals

answered Jul 8, 2023 at 9:27

3 votes

Set theory: fixed points of $n \mapsto \varepsilon_n$ and $n \mapsto \omega_n$

answered Mar 27, 2022 at 15:43

3 votes

What is the proof-theoretic ordinal of KPh?

answered Mar 31, 2022 at 6:16

3 votes

Accepted

A question on the size of an admissible ordinal

answered Jun 27 at 11:06

2 votes

Diagonalization over a normal function and its derivatives on transfinite ordinals

answered Jun 11, 2022 at 18:26

2 votes

What's the use of countable ordinals? (prompted by a remark of Tim Gowers)

answered Jun 13, 2023 at 23:19

2 votes

What are some examples of colorful language in serious mathematics papers?

answered Mar 4 at 9:59

2 votes

Which ordinals can be proof-theoretic ordinals of a reasonable theory?

answered Jun 21 at 10:08

1 vote

Why can't $L_\beta$ contain a real coding a well-ordering of order-type $\beta$, when $\beta$ is a gap ordinal?

answered May 1 at 4:06

1 vote

Accepted

End elementary extension in infinitary logic of some $L_\alpha$ producing a $L_\beta$

answered Mar 21 at 5:58

1 vote

Can this form of reflection be consistent?

answered Feb 25 at 8:03

1 vote

Accepted

Minimal models in strong set theories - pt. 2

answered Feb 1 at 6:47

1 vote

How closely do ordinal collapsing functions relate to Mostowski collapse?

answered Jul 6, 2023 at 6:06

1 vote

How to solve this exercise about large countable ordinals?

answered Aug 15, 2023 at 19:19

1 vote

What's the order type of the following set?

answered Aug 26, 2023 at 23:34

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36 Answers

Finite verification for theorems due to Busy Beaver numbers

Most recent results on formulating Kunen's inconsistency theorem in ZF without choice

Smallest ordinal modelling $\aleph_1$?

Do all limit $\alpha \in \omega_1^L$ satisfy $L_\alpha \models V=HC$?

Iterated Gentzen: or, a Sith objection to the proof of consistency of PA

Important open problems that have already been reduced to a finite but infeasible amount of computation

What are some noteworthy "mic-drop" moments in math?

When is 2 qualitatively different from 3?

When is 4 qualitatively different than $n\leq 3$?

What are the known large cardinal axioms for which weaker and stronger set theories "catch up"?

Theorems with many distinct proofs

How can I catalog these generalized Collatz problems?

Harvey Friedman: The expanding mind

End-extension in Gödel's constructible universe

Is all ordinary mathematics contained in high school mathematics?

Parameter-free effective cardinals

Set theory: fixed points of $n \mapsto \varepsilon_n$ and $n \mapsto \omega_n$

What is the proof-theoretic ordinal of KPh?

A question on the size of an admissible ordinal

Diagonalization over a normal function and its derivatives on transfinite ordinals

What's the use of countable ordinals? (prompted by a remark of Tim Gowers)

What are some examples of colorful language in serious mathematics papers?

Which ordinals can be proof-theoretic ordinals of a reasonable theory?

Why can't $L_\beta$ contain a real coding a well-ordering of order-type $\beta$, when $\beta$ is a gap ordinal?

End elementary extension in infinitary logic of some $L_\alpha$ producing a $L_\beta$

Can this form of reflection be consistent?

Minimal models in strong set theories - pt. 2

How closely do ordinal collapsing functions relate to Mostowski collapse?

How to solve this exercise about large countable ordinals?

What's the order type of the following set?