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Joel David Hamkins's user avatar
Joel David Hamkins's user avatar
Joel David Hamkins's user avatar
Joel David Hamkins
  • Member for 15 years, 1 month
  • Last seen this week
45 votes
Accepted

Does every series of hyperreal numbers converge to some hyperreal number?

44 votes

What are the most attractive Turing undecidable problems in mathematics?

44 votes
Accepted

Writing "Semi-Formal" Proofs

43 votes
Accepted

Arithmetic fixed point theorem

43 votes
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Cardinality: Why is there no "ℵ½"?

43 votes

If any open set is a countable union of balls, does it imply separability?

43 votes

What is the most "concrete-feeling" equivalent formulation of the Continuum Hypothesis that you can think of?

43 votes
Accepted

Why hasn't mereology succeeded as an alternative to set theory?

42 votes
Accepted

Who wins two player sudoku?

42 votes
Accepted

Research topics restricted to students at top universities?

41 votes
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How far is Lindelöf from compactness?

41 votes

Are some numbers more irrational than others?

41 votes
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Are all sets totally ordered ?

40 votes
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Has decidability got something to do with primes?

39 votes
Accepted

In set theories where Continuum Hypothesis is false, what are the new sets?

39 votes

Basic results with three or more hypotheses

39 votes

True by accident (and therefore not amenable to proof)

39 votes

Decidability of chess on an infinite board

39 votes

What do named "tricks" share?

39 votes

Do set-theorists use informal set theory as their meta-theory when talking about models of ZFC?

39 votes
Accepted

What is known about the theory of natural numbers with only 0, successor and max?

38 votes
Accepted

Is there a position in infinite Go for which the life of a particular stone has transfinite game value?

38 votes
Accepted

How to add essentially new knots to the universe?

37 votes
Accepted

What is the cofinality of the co-infinite subsets of ${\bf N}$?

37 votes

What do you do if you believe a problem is undecidable?

37 votes
Accepted

Is there a computable model of ZFC?

37 votes
Accepted

Is the theory of categories decidable?

37 votes
Accepted

Is it necessary that model of theory is a set?

37 votes

What are the most elegant proofs that you have learned from MO?

37 votes

Examples of interesting false proofs

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