User Will Brian

123 votes

Tweetable Mathematics

answered Apr 26, 2017 at 14:21

66 votes

Accepted

Bijection from the plane to itself that sends circles to squares

answered Apr 10, 2017 at 19:35

46 votes

When can one continuously prescribe a unit vector orthogonal to a given orthonormal system?

answered Nov 5, 2018 at 15:48

43 votes

Accepted

Which popular games have been studied mathematically?

answered Jan 9, 2018 at 22:11

40 votes

Accepted

A topology on $\Bbb R$ where the compact sets are precisely the countable sets

answered Nov 21, 2016 at 20:29

39 votes

Accepted

Are all free ultrafilters 'the same' in some sense?

answered Dec 10, 2021 at 13:51

30 votes

Proofs where higher dimension or cardinality actually enabled much simpler proof?

answered May 21, 2020 at 12:59

29 votes

Is it possible to define higher cardinal arithmetics

answered Aug 18, 2016 at 15:30

27 votes

Accepted

Does the axiom of choice follow from the statement "Every simple undirected graph is either connected, or its complement is connected"?

answered Apr 9, 2018 at 12:57

27 votes

Accepted

A metric characterization of the real line

answered Mar 16, 2023 at 18:07

26 votes

Can you partition the sphere into orthonormal bases?

answered Sep 30, 2021 at 17:15

26 votes

Unnecessary uses of the Continuum Hypothesis

answered Feb 22, 2022 at 20:04

23 votes

Accepted

Can random variables that almost surely solve equations be repaired to surely solve these equations?

answered Nov 26, 2019 at 19:57

23 votes

Accepted

Continuous images of $\beta \mathbb{N} \setminus\mathbb{N}$

answered Mar 21, 2018 at 1:40

20 votes

Accepted

Is $[0,1]$ a disjoint union of $\aleph_1$ compact subsets with empty interior?

answered Feb 1, 2018 at 13:52

20 votes

Continuous bijections vs. Homeomorphisms

answered Apr 16, 2015 at 20:57

20 votes

Accepted

Can an injective $f: \Bbb{R}^m \to \Bbb{R}^n$ have a closed graph for $m>n$?

answered Aug 2, 2018 at 20:34

17 votes

Accepted

Is there a known condition for partial sums of a decreasing positive sequence to take all values up to the total sum?

answered May 25, 2020 at 19:16

17 votes

Is every function $f: \mathbb R \to \mathbb R$ differentiable at at least one point when restricted to some everywhere dense subset of $\mathbb R$?

answered Apr 2, 2020 at 15:15

16 votes

Example of an uncountable scattered space with some properties

answered Feb 22, 2022 at 14:36

16 votes

Accepted

Ultrafilter subtraction and "zero"

answered Jul 29, 2022 at 4:57

16 votes

Near permutation $n\mapsto n+1$ not conjugate to its inverse on the Stone-Čech remainder?

answered Feb 18, 2020 at 16:20

16 votes

Necessary use of large cardinals in mathematics

answered Jan 15, 2020 at 14:03

16 votes

Accepted

Packing obtuse vectors in $\mathbb{R}^d$

answered Jun 5, 2015 at 1:35

15 votes

Accepted

Can two-point sets be Borel?

answered Jun 20, 2017 at 16:57

15 votes

Accepted

Does the class of Hausdorff spaces have a shared "Coordinate space"?

answered Jan 23, 2017 at 17:06

15 votes

Accepted

How “disconnected” can a continuum be?

answered Jan 11, 2023 at 14:27

15 votes

Accepted

Partitions of the real line into Borel subsets

answered May 11, 2021 at 23:02

14 votes

Accepted

On the Large Cardinal Strength of Normal Moore Space Conjecture

answered Jul 20, 2018 at 12:45

14 votes

Is there a subset of the plane that meets every line in two open intervals?

answered Jul 10, 2015 at 16:02

Stack Exchange Network

167 Answers

Tweetable Mathematics

Bijection from the plane to itself that sends circles to squares

When can one continuously prescribe a unit vector orthogonal to a given orthonormal system?

Which popular games have been studied mathematically?

A topology on $\Bbb R$ where the compact sets are precisely the countable sets

Are all free ultrafilters 'the same' in some sense?

Proofs where higher dimension or cardinality actually enabled much simpler proof?

Is it possible to define higher cardinal arithmetics

Does the axiom of choice follow from the statement "Every simple undirected graph is either connected, or its complement is connected"?

A metric characterization of the real line

Can you partition the sphere into orthonormal bases?

Unnecessary uses of the Continuum Hypothesis

Can random variables that almost surely solve equations be repaired to surely solve these equations?

Continuous images of $\beta \mathbb{N} \setminus\mathbb{N}$

Is $[0,1]$ a disjoint union of $\aleph_1$ compact subsets with empty interior?

Continuous bijections vs. Homeomorphisms

Can an injective $f: \Bbb{R}^m \to \Bbb{R}^n$ have a closed graph for $m>n$?

Is there a known condition for partial sums of a decreasing positive sequence to take all values up to the total sum?

Is every function $f: \mathbb R \to \mathbb R$ differentiable at at least one point when restricted to some everywhere dense subset of $\mathbb R$?

Example of an uncountable scattered space with some properties

Ultrafilter subtraction and "zero"

Near permutation $n\mapsto n+1$ not conjugate to its inverse on the Stone-Čech remainder?

Necessary use of large cardinals in mathematics

Packing obtuse vectors in $\mathbb{R}^d$

Can two-point sets be Borel?

Does the class of Hausdorff spaces have a shared "Coordinate space"?

How “disconnected” can a continuum be?

Partitions of the real line into Borel subsets

On the Large Cardinal Strength of Normal Moore Space Conjecture

Is there a subset of the plane that meets every line in two open intervals?