130

Questions

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1

1

vote

1

answer

179

views

An action or two of $SL_2(\Bbb Z)$?

gr.group-theory hyperbolic-geometry

apr 25 at 7:54 Artur Jackson 11●3

1

14

votes

3

answers

766

views

Research level applications of “row rank = column rank”?

linear-algebra teaching big-list big-picture

feb 28 at 20:01 David Feldman 11.3k●2●25●79

2

11

votes

3

answers

993

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Cantor’s diagonal argument and ZF

set-theory axiom-of-choice

feb 27 at 18:15 François G. Dorais♦ 22.4k●2●48●113

6

10

votes

3

answers

807

views

Games that never begin

descriptive-set-theory set-theory

nov 13 at 13:51 Joel David Hamkins 74.9k●7●187●343

11

28

votes

11

answers

2k

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

big-list open-problem computation open-problems-list

nov 14 at 9:06 Nick Gill 2,881●7●18

6

18

votes

3

answers

467

views

An equivalence relation on group actions

gr.group-theory

oct 27 at 12:28 Yves Cornulier 2,916●1●6●11

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4

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0

answers

129

views

Almost universal properties

ct.category-theory descriptive-set-theory

oct 24 at 19:58 David Feldman 11.3k●2●25●79

1

7

votes

0

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384

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Is every $\sigma$-algebra of sets abstractly the Borel algebra of a topology on perhps some other set?

gn.general-topology set-theory descriptive-set-theory measure-theory

oct 15 at 1:23 Joel David Hamkins 74.9k●7●187●343

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5

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0

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209

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Closure properties of familes of $G_\delta$ sets.

descriptive-set-theory gn.general-topology set-theory

oct 8 at 23:05 David Feldman 11.3k●2●25●79

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8

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0

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418

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In ZF, when is a disjoint union of metrizable spaces metrizable?

gn.general-topology metric-spaces set-theory axiom-of-choice

sep 22 at 0:05 Joel David Hamkins 74.9k●7●187●343