User Joel David Hamkins

9 votes

1 answer

544 views

Can there be a tree of height $\omega_2$ having all levels countable, with no cofinal branch?

asked May 30, 2015 at 3:51

9 votes

2 answers

498 views

Can a parent and child node have the same type in a well-founded digraph tree?

asked Nov 18, 2014 at 13:38

9 votes

3 answers

710 views

What is the optimal size in the finite axiom of symmetry?

asked Apr 12, 2016 at 2:31

9 votes

3 answers

1k views

The Sudoku game: Solver-Spoiler variation

asked Apr 17, 2018 at 14:34

8 votes

1 answer

769 views

Can $V\neq\text{HOD}$ if every $\Sigma_2$-definable set has an ordinal-definable element?

asked Sep 14, 2014 at 0:46

8 votes

4 answers

941 views

Are there two computable binary trees such that each has a branch not computing any branch through the other?

asked Feb 13, 2014 at 4:53

7 votes

2 answers

735 views

For a partition of $\mathbb{R}$ into countably infinite sets, must there be an almost-disjoint family of $2^{\frak c}$ many selectors?

asked Mar 20, 2015 at 14:27

7 votes

1 answer

578 views

Are the definable hyper-reals, using quantifiers only over the standard reals and natural numbers, the same as the algebraic numbers?

asked Feb 3, 2017 at 23:55

7 votes

1 answer

572 views

Finding a PA cut in a nonstandard model of PA

asked Dec 3, 2017 at 13:53

7 votes

1 answer

494 views

Normal form for terms in language with two ring structures

asked Aug 3, 2023 at 1:39

6 votes

1 answer

372 views

Is $n$ uniformly computable from an oracle for the $n^{\rm th}$ jump $0^{(n)}$?

asked Aug 24, 2017 at 17:16

6 votes

1 answer

626 views

Can $H_{\omega_1}$ and $H_{\omega_2}$ be in bi-interpretation synonymy?

asked Jan 16, 2020 at 8:36

5 votes

0 answers

140 views

How big is the smallest nontrivial partition of the unit interval into closed disjoint closed sets? [duplicate]

asked Apr 10, 2018 at 22:28

2 votes

0 answers

149 views

Does the Lévy collapse obey this nice characterization? [duplicate]

asked Mar 6, 2014 at 15:46

Stack Exchange Network

104 Questions

Can there be a tree of height $\omega_2$ having all levels countable, with no cofinal branch?

Can a parent and child node have the same type in a well-founded digraph tree?

What is the optimal size in the finite axiom of symmetry?

The Sudoku game: Solver-Spoiler variation

Can $V\neq\text{HOD}$ if every $\Sigma_2$-definable set has an ordinal-definable element?

Are there two computable binary trees such that each has a branch not computing any branch through the other?

For a partition of $\mathbb{R}$ into countably infinite sets, must there be an almost-disjoint family of $2^{\frak c}$ many selectors?

Are the definable hyper-reals, using quantifiers only over the standard reals and natural numbers, the same as the algebraic numbers?

Finding a PA cut in a nonstandard model of PA

Normal form for terms in language with two ring structures

Is $n$ uniformly computable from an oracle for the $n^{\rm th}$ jump $0^{(n)}$?

Can $H_{\omega_1}$ and $H_{\omega_2}$ be in bi-interpretation synonymy?

How big is the smallest nontrivial partition of the unit interval into closed disjoint closed sets? [duplicate]

Does the Lévy collapse obey this nice characterization? [duplicate]