488

Answers

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17

Is choice needed to establish the existence of idempotent ultrafilters?

17

Axiom to exclude nonstandard natural numbers

16

How many models of Peano arithmetic are isomorphic to the standard model and how many models of Peano arithmetic are non-standard?

15

Why do we ignore non-standard finite sets in ordinary mathematics?

15

Is a random subset of the real numbers non-measurable? Is the set of measurable sets measurable?

15

matrices whose entries sum to zero

15

Proper classes and their consequences

15

Reasons to believe Vopenka’s principle/huge cardinals are consistent

15

Can the symmetric groups on sets of different cardinalities be isomorphic?

15

What is a category of sets?

15

Which Turing machines accept the language of trivial words in a finitely presented group?

15

Why hasn’t mereology suceeded as an alternative to set theory?

14

About the proof of the proposition “there exists irrational numbers a, b such that a^b is rational”

14

Reference Request: Independence of the ultrafilter lemma from ZF

14

Mathematical ideas named after places (3)

14

What’s so “schematic” about schemes?

14

When does Cantor-Bernstein hold?

14

Locally compact Hausdorff space that is not normal

14

Does constructing non-measurable sets require the axiom of choice?

14

How would set theory research be affected by using ETCS instead of ZFC?

13

Understanding Specker’s disproof of the axiom of choice in New Foundations

13

What is the status of irrational numbers within finitism/ultrafinitism?

13

ULTRAINFINITISM, or a step beyond the transfinite

13

Fraktur symbols for Lie algebras: $\mathfrak{g}$, etc.

13

Aut(G) = $C_3$, G = ?

13

Can breadth hurt a job candidate?

13

Why are the integers with the cofinite topology not path-connected?

13

Bourbaki’s epsilon-calculus notation

13

Continuously selecting elements from unordered pairs

13

Occurence of trivial representation in a tensor square.