User Joel David Hamkins

32 votes

Accepted

Are the real numbers isomorphic to a nontrivial ultraproduct of fields?

answered Mar 29 at 19:24

31 votes

How far wrong could the Continuum Hypothesis be?

answered Sep 16, 2015 at 2:50

31 votes

Set theoretical multiverse and truths

answered Nov 3, 2017 at 1:48

31 votes

Interesting examples of vacuous / void entities

answered Nov 14, 2010 at 0:17

31 votes

Recent claim that inaccessibles are inconsistent with ZF

answered Aug 20, 2011 at 1:28

31 votes

What could be some potentially useful mathematical databases?

answered Jun 21, 2011 at 22:34

31 votes

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Intermediate value theorem on computable reals

answered Dec 16, 2009 at 18:19

31 votes

Which graphs are Cayley graphs?

answered Feb 12, 2010 at 13:17

31 votes

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Is non-existence of the hyperreals consistent with ZF?

answered Dec 4, 2014 at 2:17

31 votes

Why does CH imply that there is a unique ultrapower of $\mathbb{N}$?

answered Jul 15, 2013 at 2:13

31 votes

Are the two meanings of "undecidable" related?

answered May 16, 2013 at 10:44

30 votes

Is the Invariant Subspace Problem arithmetic?

answered Jun 4, 2014 at 22:59

30 votes

What is your favorite "strange" function?

answered Apr 22, 2010 at 19:14

30 votes

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Injectivity of cardinality of power set

answered Jun 10, 2011 at 22:06

30 votes

Should there be a true model of set theory?

answered Nov 6, 2010 at 11:44

30 votes

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Human checkable proof of the Four Color Theorem?

answered Nov 3, 2010 at 14:25

30 votes

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Gödel's Incompleteness Theorem and the complexity of arithmetic

answered Sep 3, 2010 at 10:26

30 votes

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Why should we care about "higher infinities" outside of set theory?

answered Aug 27, 2015 at 7:22

30 votes

Countable path-connected Hausdorff space

answered Aug 11, 2015 at 15:27

30 votes

Nonequivalent definitions in Mathematics

answered Nov 22, 2017 at 21:58

30 votes

Applications of Zorn’s lemma that aren’t chain-complete/directed-complete?

answered Apr 18, 2021 at 19:31

29 votes

Should axiomatic set theory be translated into graph theory?

answered Jan 6, 2016 at 12:27

29 votes

Accepted

What are the advantages of the more abstract approaches to nonstandard analysis?

answered Dec 17, 2015 at 22:55

29 votes

How to solve $f(f(x)) = \cos(x)$?

answered Mar 9, 2010 at 15:10

29 votes

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V=L and a Well-Ordering of the Reals

answered Nov 23, 2009 at 18:10

29 votes

Accepted

Definable collections without definable members (in ZF)

answered Jan 1, 2010 at 23:37

29 votes

Infinite mathematics as non-standard finite mathematics?

answered Mar 4, 2012 at 0:25

28 votes

Ultrainfinitism, or a step beyond the transfinite

answered Jun 30, 2012 at 0:36

28 votes

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The reals as continuous image of the irrationals

answered Nov 11, 2012 at 23:38

28 votes

Illustrating Edward Nelson's Worldview with Nonstandard Models of Arithmetic

answered Sep 20, 2013 at 9:32

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1,913 Answers

Are the real numbers isomorphic to a nontrivial ultraproduct of fields?

How far wrong could the Continuum Hypothesis be?

Set theoretical multiverse and truths

Interesting examples of vacuous / void entities

Recent claim that inaccessibles are inconsistent with ZF

What could be some potentially useful mathematical databases?

Intermediate value theorem on computable reals

Which graphs are Cayley graphs?

Is non-existence of the hyperreals consistent with ZF?

Why does CH imply that there is a unique ultrapower of $\mathbb{N}$?

Are the two meanings of "undecidable" related?

Is the Invariant Subspace Problem arithmetic?

What is your favorite "strange" function?

Injectivity of cardinality of power set

Should there be a true model of set theory?

Human checkable proof of the Four Color Theorem?

Gödel's Incompleteness Theorem and the complexity of arithmetic

Why should we care about "higher infinities" outside of set theory?

Countable path-connected Hausdorff space

Nonequivalent definitions in Mathematics

Applications of Zorn’s lemma that aren’t chain-complete/directed-complete?

Should axiomatic set theory be translated into graph theory?

What are the advantages of the more abstract approaches to nonstandard analysis?

How to solve $f(f(x)) = \cos(x)$?

V=L and a Well-Ordering of the Reals

Definable collections without definable members (in ZF)

Infinite mathematics as non-standard finite mathematics?

Ultrainfinitism, or a step beyond the transfinite

The reals as continuous image of the irrationals

Illustrating Edward Nelson's Worldview with Nonstandard Models of Arithmetic