User Gro-Tsen

68 votes

'Obvious' theorems that are actually false

answered Jun 5, 2014 at 20:58

48 votes

Accepted

Can $x^{x^{x^x}}$ be a rational number?

answered Jul 10, 2013 at 18:37

44 votes

Accepted

Fibonacci number that ends with 2014 zeros?

answered Jul 20, 2014 at 21:13

18 votes

Accepted

Is the tensor product over $B$ of two flat $A$-modules flat over $A$?

answered Mar 26, 2016 at 0:21

16 votes

How to formulate the P v.s. NP problem as a formal statement inside the language of set theory?

answered Apr 30, 2016 at 19:01

14 votes

Accepted

Is there an analytic function $f : \mathbb{D} → \mathbb{D}$ with $f(0) = 1/2$ and $f′(0) = 3/4?$

answered Jul 15, 2014 at 22:41

12 votes

Accepted

trigonometry with alternative parametrizations of the circle

answered Jul 17, 2014 at 16:15

11 votes

Accepted

What is necessary and/or sufficient for polynomials to provide isomorphic quotient rings?

answered Jul 16, 2014 at 22:55

8 votes

Accepted

Hausdorff dimension of a countable set

answered Dec 12, 2015 at 10:38

8 votes

Accepted

Borel set that is not countable union or intersection of open or closed sets

answered Jan 16, 2016 at 18:47

7 votes

The equation $-1 = x^2 + y^2$ in finite fields

answered Jan 16, 2016 at 19:02

7 votes

Quaternion Group as Permutation Group

answered Jul 13, 2014 at 15:43

6 votes

Regular open set whose boundary has nonzero volume.

answered Mar 6, 2019 at 14:10

6 votes

Accepted

Find all groups such that $ab=cd\implies ba=dc$.

answered Jan 17, 2016 at 19:38

6 votes

Accepted

What's true in $\mathbb{R}^4$, false in $\mathbb{R}^3$ and uninteresting in $\mathbb{R}^5$?

answered Jan 15, 2016 at 15:51

6 votes

Accepted

How to think of $R[x,y]$-modules?

answered Jan 28, 2016 at 22:00

6 votes

Continuum Hypothesis in formalized language.

answered Jan 28, 2016 at 22:53

6 votes

Accepted

About the Words "recursion" and "recursive"

answered May 1, 2016 at 18:52

5 votes

Example of an uncountable subset of $[0,1]$ with no uncountable closed subsets

answered May 8, 2016 at 18:36

5 votes

Equality of $p$-adic fields

answered Feb 26, 2016 at 22:25

5 votes

Is $f(x)=\frac{1}{q}$ for $x=\frac{p}{q}$ and $f(x)=0$ else integrable?

answered Jan 12, 2016 at 19:08

5 votes

Accepted

Alternative set theories?

answered Jul 24, 2014 at 16:58

5 votes

The smallest infinity and the axiom of choice

answered Jan 19, 2016 at 13:03

5 votes

Accepted

What are some examples of non-commutative monoids that are both idempotent and self-distributive (on both sides)?

answered Jul 15, 2014 at 23:11

5 votes

False beliefs about Lebesgue measure on $\mathbb{R}$

answered Jan 16, 2016 at 6:31

5 votes

Accepted

Which voting method is the most fair?

answered Jul 21, 2014 at 14:51

4 votes

Galois closure of $\mathbb{C}(T,\sqrt{T^2+T+1})$ over $\mathbb{C}(T^3)$

answered Jul 16, 2014 at 17:39

4 votes

Accepted

Completeness theorem for intuitionistic logic

answered Jun 29, 2014 at 14:26

4 votes

Computable extension to $Σ_1$-sound system that is $Σ_2$-unsound?

answered Dec 23, 2017 at 23:49

3 votes

Description of projective and injective tensor products $\ell^2 \otimes \ell^2$?

answered Dec 19, 2018 at 13:45

Stack Exchange Network

67 Answers

'Obvious' theorems that are actually false

Can $x^{x^{x^x}}$ be a rational number?

Fibonacci number that ends with 2014 zeros?

Is the tensor product over $B$ of two flat $A$-modules flat over $A$?

How to formulate the P v.s. NP problem as a formal statement inside the language of set theory?

Is there an analytic function $f : \mathbb{D} → \mathbb{D}$ with $f(0) = 1/2$ and $f′(0) = 3/4?$

trigonometry with alternative parametrizations of the circle

What is necessary and/or sufficient for polynomials to provide isomorphic quotient rings?

Hausdorff dimension of a countable set

Borel set that is not countable union or intersection of open or closed sets

The equation $-1 = x^2 + y^2$ in finite fields

Quaternion Group as Permutation Group

Regular open set whose boundary has nonzero volume.

Find all groups such that $ab=cd\implies ba=dc$.

What's true in $\mathbb{R}^4$, false in $\mathbb{R}^3$ and uninteresting in $\mathbb{R}^5$?

How to think of $R[x,y]$-modules?

Continuum Hypothesis in formalized language.

About the Words "recursion" and "recursive"

Example of an uncountable subset of $[0,1]$ with no uncountable closed subsets

Equality of $p$-adic fields

Is $f(x)=\frac{1}{q}$ for $x=\frac{p}{q}$ and $f(x)=0$ else integrable?

Alternative set theories?

The smallest infinity and the axiom of choice

What are some examples of non-commutative monoids that are both idempotent and self-distributive (on both sides)?

False beliefs about Lebesgue measure on $\mathbb{R}$

Which voting method is the most fair?

Galois closure of $\mathbb{C}(T,\sqrt{T^2+T+1})$ over $\mathbb{C}(T^3)$

Completeness theorem for intuitionistic logic

Computable extension to $Σ_1$-sound system that is $Σ_2$-unsound?

Description of projective and injective tensor products $\ell^2 \otimes \ell^2$?