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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1

3

votes

0

answers

281

views

When is a pullback also a pushout?

category-theory

nov 12 '11 at 12:58 kjo 1,612

3

votes

3

answers

125

views

Q on (domains of) monomorphisms as “subobjects”

category-theory

sep 25 '11 at 20:00 Qiaochu Yuan 118k

2

votes

1

answer

70

views

What's wrong with this proof of unique factorization?

apr 17 at 16:57 kjo 1,612

2

votes

0

answers

52

views

Looking for a very gentle first book on number theory

elementary-number-theory reference-request

apr 17 at 0:53 kjo 1,612

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. 28k

2

votes

1

answer

89

views

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

1

2

votes

1

answer

35

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Weak convexity and continuity

analysis convex-analysis examples-counterexamples

feb 15 at 4:02 Community♦ 1

1

2

votes

0

answers

52

views

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 9,165

2

votes

2

answers

77

views

Construction of a partial order on a quotient of a coproduct

category-theory order-theory

mar 24 '12 at 22:56 kjo 1,612

2

votes

1

answer

43

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Does $\mathbf{E}$ determine $\mathbf{M}$ in an $(\mathbf{E}, \mathbf{M})$ image factorization system?

category-theory

mar 1 '12 at 17:16 Martin Brandenburg 22.9k

1

2

votes

1

answer

106

views

$\hom(C, -)(f) = \hom(C, -)(g) $ implies $ f = g$

category-theory

feb 1 '12 at 19:42 Zev Chonoles 54k

2

votes

2

answers

375

views

What is the categorical diagram for the tensor product?

category-theory tensor-products

jan 22 '12 at 20:32 kjo 1,612

1

2

votes

2

answers

395

views

How are addition and multiplication duals of each other?

duality-theorems

jan 20 '12 at 0:32 Qiaochu Yuan 118k

2

votes

1

answer

63

views

Question on order ideals

general-topology order-theory lattice-orders

jan 17 '12 at 7:16 Brian M. Scott 155k

1

2

votes

2

answers

321

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Question on pullbacks and compositions

category-theory

nov 13 '11 at 22:11 kjo 1,612

2

votes

2

answers

174

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$\psi \to (\exists x)\phi(x) \Leftrightarrow (\exists x)(\psi \to \phi(x))$, etc

logic

oct 10 '11 at 3:39 kjo 1,612

1

2

votes

1

answer

134

views

What's the category-theoretical existence proof, and name, for this morphism?

category-theory

aug 20 '11 at 10:47 Zhen Lin 21.1k

1

vote

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

views

Intuitive proof of row rank = column rank?

linear-algebra

may 6 at 15:29 somaye 2,003

1

vote

1

answer

47

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 592

1

vote

1

answer

22

views

On affine spaces, distances, angles, and coordinates

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

may 2 at 23:43 Berci 20.7k

1

vote

2

answers

47

views

Are the lengths from this recursive construction a geometric sequence?

geometry euclidean-geometry proof-theory geometric-construction

apr 16 at 14:31 kjo 1,612

1

vote

1

answer

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

1

vote

2

answers

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

1

vote

1

answer

85

views

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

statistics correlation probability

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

1

vote

0

answers

72

views

Need terminology for components of pullback/pushout squares (or of limits/colimits)

terminology category-theory

feb 25 '12 at 12:16 kjo 1,612

1

vote

1

answer

132

views

Looking for proof that ($\mathbf{E} =$ coequalizers, $\mathbf{M} =$ monos) yields an image factorization system

category-theory

jan 28 '12 at 19:15 kjo 1,612

1

vote

3

answers

214

views

On permutations of left cosets

group-theory permutations

dec 26 '11 at 16:29 kjo 1,612

1

vote

0

answers

43

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What are these real-valued functions called?

normed-spaces

nov 19 '11 at 19:23 kjo 1,612

kjo

72 Questions