User kjo - Mathematics Stack Exchange

bio	website
	location
	age
visits	member for	1 year, 11 months
	seen	yesterday
stats	profile views	249

	1,812 reputation	bio	website		visits	member for	1 year, 11 months
1422 badges		location			seen	yesterday

3

votes

1

answer

50

views

Proof of “triangles are similar iff corresponding angles are equal”

geometry

2d ago Oliver 486

5

19

votes

1

answer

158

views

Laplace, Legendre, Fourier, Hankel, Mellin, Hilbert, Borel, Z…: unified treatment of transforms?

jun 14 at 9:11 O.L. 7,228

1

2

votes

1

answer

53

views

The product as the space of functions to the coproduct

category-theory

jun 9 at 15:47 Nate Eldredge 23.3k

2

3

votes

2

answers

68

views

Representing $A \rightarrow B$ as $A \supseteq B$ [duplicate]

elementary-set-theory logic propositional-calculus

jun 7 at 13:34 Carl Mummert 26.6k

2

4

votes

1

answer

111

views

Who first defined open sets in terms of neighborhoods?

general-topology math-history

may 28 at 17:37 Henno Brandsma 11.1k

3

votes

2

answers

82

views

Error in book's definition of open sets in terms of neighborhoods?

general-topology elementary-set-theory

may 28 at 13:03 kjo 1,812

49

107

votes

23

answers

5

kviews

Can't argue with success? Looking for “bad math” that “gets away with it”

examples-counterexamples

may 24 at 22:29 Integral 1,192

0

votes

2

answers

41

views

$[(|X| \ge \aleph_0) \;\wedge\; (A \subset X) \;\wedge\; (|A| = |X\backslash A|)] \Rightarrow |A| = |X|$

elementary-set-theory cardinals

may 19 at 1:19 Marco Vergura 1,071

1

3

votes

3

answers

93

views

Do Boolean rings always have a unit element?

abstract-algebra ring-theory

may 15 at 13:27 rschwieb 22.5k

1

4

votes

2

answers

55

views

Is the kernel of a homomorphism from a Boolean ring to $\mathbb{Z}_2$ always a maximal ideal?

abstract-algebra ring-theory

may 14 at 10:04 kjo 1,812

3

votes

4

answers

83

views

shortest path to Tychonoff?

general-topology

may 9 at 2:16 Paul 4,905

1

vote

0

answers

27

views

Not every $1$-nullset is an $s$-nullset, for $0 < s < 1$

real-analysis general-topology measure-theory

may 6 at 20:07 kjo 1,812

1

vote

1

answer

53

views

Intuitive proof of row rank = column rank?

linear-algebra

may 6 at 15:29 somaye 2,296

5

votes

6

answers

270

views

Looking for math audio resources online

online-resources

may 3 at 19:33 Michelle Chen 1

1

vote

1

answer

55

views

Looking for name of theorem: “rational $\Leftrightarrow$ fractional part terminates or repeats”

elementary-number-theory arithmetic irrational-numbers rational-numbers

may 3 at 14:44 Loki Clock 838

1

vote

1

answer

25

views

On affine spaces, distances, angles, and coordinates

linear-algebra vector-spaces inner-product-space affine-geometry

may 2 at 23:43 Berci 22.3k

1

4

votes

0

answers

56

views

Partition of $\mathbb{R}$ into nullset and 1st category set

real-analysis set-theory baire-category

may 1 at 0:24 kjo 1,812

1

4

votes

2

answers

219

views

Is there a meaningful distinction between “inclusion” and “monomorphism”?

notation terminology category-theory

apr 24 at 12:56 user18921 4,090

3

votes

4

answers

54

views

$(x_1y_2 - x_2y_1)$: area or displacement?

linear-algebra

apr 21 at 4:44 Thomas Belulovich 1,361

2

votes

1

answer

73

views

What's wrong with this proof of unique factorization?

elementary-number-theory notation terminology

apr 17 at 16:57 kjo 1,812

0

votes

0

answers

26

views

What are $\sigma$ and $\tau$ in $n = 2^{\sigma(n)}\,\tau(n)$ called?

elementary-number-theory notation terminology

apr 17 at 11:48 kjo 1,812

2

votes

0

answers

56

views

Looking for a very gentle first book on number theory

elementary-number-theory reference-request

apr 17 at 0:53 kjo 1,812

0

votes

1

answer

98

views

Uniqueness of factorization for math-phobes?

elementary-number-theory

apr 16 at 18:52 Community♦ 1

0

votes

2

answers

54

views

Are the lengths from this recursive construction a geometric sequence?

geometry euclidean-geometry proof-theory geometric-construction

apr 16 at 14:31 kjo 1,812

3

votes

2

answers

68

views

$\mu(A) = 0 \;\;\; \Rightarrow \;\; \int_A f \,\, d\mu = 0$

measure-theory

apr 15 at 23:13 Christopher A. Wong 6,846

1

vote

1

answer

32

views

$\mathbb{P}(\{X>a\}) = 1 \Rightarrow \mathbb{E}(X)>a$

probability measure-theory

apr 15 at 20:08 ncmathsadist 17.5k

2

votes

3

answers

45

views

Intuition behind $(\{a, b, p, q\} \subset \mathbb{R}^{+} \;\wedge\;\; 1/p +1/q = 1) \Rightarrow a^p/p + b^q/q \geq ab$

analysis inequality

apr 11 at 1:21 N. S. 30.6k

1

vote

2

answers

42

views

Interpreting $\mathrm{Var}(\overline{X}) = \mathrm{Cov}(X_i, \overline{X})$

linear-algebra probability statistics

apr 8 at 11:57 kjo 1,812

10

votes

3

answers

149

views

Finding a more direct way to reach $\mathbb{E} \left( \sum (X_i - \mu)^2 \right) - \mathbb{E} \left( \sum (X_i - \overline{X})^2 \right) = \sigma^2$

probability statistics

apr 7 at 18:29 kjo 1,812

4

votes

3

answers

77

views

Notation for $X - \mathbb{E}(X)$?

probability statistics notation convention

apr 7 at 15:41 Michael Hardy 51.2k

kjo

78 Questions