User Szmagpie

10 votes

2 answers

8k views

Fundamental group of a wedge sum, in general (e.g. when van Kampen does not apply)

asked Apr 26, 2016 at 22:00

9 votes

2 answers

12k views

Expected value of $\max\{X_1,\ldots,X_n\}$ where $X_i$ are iid uniform. [duplicate]

asked Jun 6, 2016 at 3:10

6 votes

1 answer

362 views

Which surface is homotopy equivalent to $\Bbb{R}^4$ minus the planes $x=y=0$, $z=w=0$?

asked Apr 19, 2016 at 21:49

6 votes

0 answers

2k views

Expected number of cycles of length $k$ in a random graph. My simple (too simple?) solution

asked May 24, 2016 at 4:05

5 votes

1 answer

267 views

True or False: there is a space $X$ such that $S^1$ is homeomorphic to $X\times X$

asked Apr 27, 2016 at 16:04

5 votes

1 answer

747 views

What is a probability distribution?

asked Mar 9, 2016 at 16:51

5 votes

2 answers

646 views

Completeness of product measure

asked Mar 29, 2016 at 17:58

5 votes

1 answer

1k views

Quantification over the set(?) of predicates

asked Apr 3, 2016 at 15:45

5 votes

1 answer

2k views

Convolution of PDFs is a PDF

asked Jun 10, 2016 at 6:04

4 votes

1 answer

737 views

Axiom of Choice implies the Well-Ordering Principle

asked May 3, 2016 at 23:49

4 votes

2 answers

589 views

Construction of a finite projective plane of order $p$, for any prime $p$

asked May 22, 2016 at 16:15

4 votes

1 answer

799 views

For every group $G$ there is a $2$-dimensional cell complex $X_G$ with $\pi_1(X_G)\cong G$.

asked Apr 18, 2016 at 16:37

4 votes

1 answer

613 views

What does Robinson's overspill lemma tell us?

asked Nov 17, 2016 at 19:22

3 votes

1 answer

380 views

Are 'numerals' closed under exponentiation?

asked Oct 24, 2016 at 13:45

3 votes

0 answers

145 views

Degree sequences of split graphs

asked Nov 1, 2016 at 18:26

3 votes

1 answer

164 views

First Incompleteness Theorem: Does the limit of $\mathsf{T}_n\cup\{\rho_{\mathsf{T}_n}\}$ exist?

asked Mar 18, 2016 at 19:30

3 votes

1 answer

1k views

Hatcher's proof of the van Kampen Theorem (injectivity of $\Phi$ – unique factorizations of $[f]$)

asked Apr 22, 2016 at 0:22

3 votes

3 answers

1k views

The problem of Free Variables in natural deduction rules ($\forall$, $\exists$, =).

asked Jun 5, 2015 at 14:23

3 votes

0 answers

1k views

The relationship between random variables, distribution functions and probability measures

asked May 16, 2016 at 15:17

3 votes

1 answer

833 views

Why do we use Dedekind cuts to define the real numbers?

asked Sep 27, 2016 at 18:40

2 votes

1 answer

71 views

Show that $3\cdot |A|<9^{|A|}$ for every $A$

asked May 4, 2016 at 23:35

2 votes

1 answer

92 views

Characteristic functions proof... $\mu\{x:|x|>r\}\le\tfrac r2\int_{-2/r}^{2/r}(1-\varphi(t))\,dt$

asked May 3, 2016 at 0:10

2 votes

1 answer

81 views

Integrating a linear-map valued function

asked Jun 3, 2015 at 11:55

2 votes

1 answer

100 views

Motivation for the (arithmetic) 'collection axioms' $B\varphi$

asked Dec 9, 2016 at 19:23

2 votes

0 answers

454 views

Can you rearrange terms in an infinite series without affecting the convergence?

asked Jan 10, 2017 at 15:45

2 votes

2 answers

351 views

Formally coding finite combinatorics/number theory in Peano arithmetic

asked Mar 31, 2017 at 21:44

1 vote

2 answers

145 views

Under what conditions does $\lim (a_n)^{1/n}$ converge?

asked Nov 7, 2016 at 20:28

1 vote

0 answers

53 views

If the series $\sum_{k=1}^\infty a_k$ diverges, must $\sum_{k=1}^\infty (g(k+1)-g(k))a_{g(k)}$ also diverge?

asked Dec 2, 2016 at 15:51

1 vote

2 answers

846 views

Size of the deck transformation group

asked Nov 15, 2015 at 20:39

1 vote

1 answer

73 views

Set theory: $\forall A\;\mathcal{P}(\bigcup A)\notin A$

asked Apr 3, 2016 at 19:56

Stack Exchange Network

50 Questions

Fundamental group of a wedge sum, in general (e.g. when van Kampen does not apply)

Expected value of $\max\{X_1,\ldots,X_n\}$ where $X_i$ are iid uniform. [duplicate]

Which surface is homotopy equivalent to $\Bbb{R}^4$ minus the planes $x=y=0$, $z=w=0$?

Expected number of cycles of length $k$ in a random graph. My simple (too simple?) solution

True or False: there is a space $X$ such that $S^1$ is homeomorphic to $X\times X$

What is a probability distribution?

Completeness of product measure

Quantification over the set(?) of predicates

Convolution of PDFs is a PDF

Axiom of Choice implies the Well-Ordering Principle

Construction of a finite projective plane of order $p$, for any prime $p$

For every group $G$ there is a $2$-dimensional cell complex $X_G$ with $\pi_1(X_G)\cong G$.

What does Robinson's overspill lemma tell us?

Are 'numerals' closed under exponentiation?

Degree sequences of split graphs

First Incompleteness Theorem: Does the limit of $\mathsf{T}_n\cup\{\rho_{\mathsf{T}_n}\}$ exist?

Hatcher's proof of the van Kampen Theorem (injectivity of $\Phi$ – unique factorizations of $[f]$)

The problem of Free Variables in natural deduction rules ($\forall$, $\exists$, =).

The relationship between random variables, distribution functions and probability measures

Why do we use Dedekind cuts to define the real numbers?

Show that $3\cdot |A|<9^{|A|}$ for every $A$

Characteristic functions proof... $\mu\{x:|x|>r\}\le\tfrac r2\int_{-2/r}^{2/r}(1-\varphi(t))\,dt$

Integrating a linear-map valued function

Motivation for the (arithmetic) 'collection axioms' $B\varphi$

Can you rearrange terms in an infinite series without affecting the convergence?

Formally coding finite combinatorics/number theory in Peano arithmetic

Under what conditions does $\lim (a_n)^{1/n}$ converge?

If the series $\sum_{k=1}^\infty a_k$ diverges, must $\sum_{k=1}^\infty (g(k+1)-g(k))a_{g(k)}$ also diverge?

Size of the deck transformation group

Set theory: $\forall A\;\mathcal{P}(\bigcup A)\notin A$