User kjo - Mathematics Stack Exchange

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	1,612 reputation	bio	website		visits	member for	1 year, 10 months
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$[(|X| \ge \aleph_0) \;\wedge\; (A \subset X) \;\wedge\; (|A| = |X\backslash A|)] \Rightarrow |A| = |X|$

elementary-set-theory cardinals

may 19 at 1:19 Marco Vergura 717

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3

votes

3

answers

82

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Do Boolean rings always have a unit element?

abstract-algebra ring-theory

may 15 at 13:27 rschwieb 21k

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4

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2

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51

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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 1,612

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votes

4

answers

76

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shortest path to Tychonoff?

general-topology

may 9 at 2:16 Paul 3,802

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0

answers

25

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

real-analysis general-topology measure-theory

may 6 at 20:07 kjo 1,612

1

vote

1

answer

40

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Intuitive proof of row rank = column rank?

linear-algebra

may 6 at 15:29 somaye 2,003

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vote

1

answer

47

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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 592

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vote

1

answer

22

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On affine spaces, distances, angles, and coordinates

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

may 2 at 23:43 Berci 20.7k

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4

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0

answers

54

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

real-analysis set-theory baire-category

may 1 at 0:24 kjo 1,612

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votes

4

answers

54

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

linear-algebra

apr 21 at 4:44 Thomas Belulovich 1,311

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1

answer

70

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What's wrong with this proof of unique factorization?

elementary-number-theory notation terminology

apr 17 at 16:57 kjo 1,612

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

elementary-number-theory notation terminology

apr 17 at 11:48 kjo 1,612

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0

answers

52

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Looking for a very gentle first book on number theory

elementary-number-theory reference-request

apr 17 at 0:53 kjo 1,612

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votes

1

answer

92

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Uniqueness of factorization for math-phobes?

elementary-number-theory

apr 16 at 18:52 Community♦ 1

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2

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47

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Are the lengths from this recursive construction a geometric sequence?

geometry euclidean-geometry proof-theory geometric-construction

apr 16 at 14:31 kjo 1,612

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2

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67

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

measure-theory

apr 15 at 23:13 Christopher A. Wong 6,541

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1

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31

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

probability measure-theory

apr 15 at 20:08 ncmathsadist 17.2k

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3

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45

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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. 28k

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2

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41

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

linear-algebra probability statistics

apr 8 at 11:57 kjo 1,612

4

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3

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76

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

probability statistics notation convention

apr 7 at 15:41 Michael Hardy 48.2k

10

votes

3

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146

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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 1,612

2

votes

1

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89

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Questions about Hamel basis for ${\mathbb R}$ over ${\mathbb Q}$

linear-algebra abstract-algebra vector-spaces

feb 16 at 15:20 Henning Makholm 53.6k

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1

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35

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Weak convexity and continuity

analysis convex-analysis examples-counterexamples

feb 15 at 4:02 Community♦ 1

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0

answers

52

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Interpretation of the Laplace transform

real-analysis complex-analysis analysis fourier-analysis laplace-transform

feb 10 at 2:52 kjo 1,612

2

votes

5

answers

118

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Looking for proof of $\sum_1^n \alpha_i x^i = 0 \;\; \Longrightarrow \;\; \alpha_i = 0, \forall\;i$.

linear-algebra

feb 3 at 9:18 YACP 9,190

3

votes

2

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131

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Looking for a bijective nowhere-continuous function ${\mathbb R}\rightarrow{\mathbb R}$

real-analysis general-topology examples-counterexamples

feb 3 at 11:37 Alessandro 71

4

14

votes

5

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204

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Looking for Cover's hubris-busting ${\mathbb R}^{N\gg3}$ counterexamples

general-topology intuition examples-counterexamples dimension-theory

feb 2 at 14:36 kjo 1,612

45

101

votes

23

answers

5

kviews

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

examples-counterexamples

apr 3 at 15:45 Inceptio 4,785

1

vote

1

answer

85

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In search of memorable example of “(Pearson-)uncorrelated $\not\Rightarrow$ independent”

statistics correlation probability

mar 18 '12 at 5:10 EMS 1,139

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4

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1

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149

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Need construction for coequalizer in $\mathbf{Poset}$

category-theory order-theory

jul 22 at 2:53 Qiaochu Yuan 118k

kjo

72 Questions