User David Toth - Mathematics Stack Exchange

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	545 reputation	bio	website	tothchat.com	visits	member for	1 year
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1

8

votes

2

answers

119

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Can we expand numbers on the left to produce irrational numbers?

elementary-set-theory number-systems

mar 28 at 14:24 Asaf Karagila 91.8k

6

votes

1

answer

58

views

If $S_n$ is a symmetric group, what is the name for $n$?

apr 14 at 1:13 amWhy 55.4k

1

5

votes

1

answer

183

views

What is $\aleph_0$ powered to $\aleph_0$?

set-theory cardinals

aug 17 at 6:01 Asaf Karagila 91.8k

4

votes

3

answers

104

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What is the automorphism group of $\mathbb{R}$ under addition? [duplicate]

abstract-algebra group-theory abelian-groups

feb 23 at 18:09 Asaf Karagila 91.8k

1

3

votes

1

answer

88

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$\pi_1(X)$ finite, show $f:X \to S^1$ is nullhomotopic

algebraic-topology

may 3 at 15:56 Justin Young 950

1

3

votes

2

answers

77

views

What is the necessary and sufficient condition for a CW-complex to have its homology groups torsion-free?

reference-request algebraic-topology

apr 23 at 19:23 Pete L. Clark 44.7k

2

3

votes

1

answer

63

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Show a subspace formed by a Klein bottle is homotopy-equivalent to $S^1 \vee S^1 \vee S^2$

algebraic-topology

apr 23 at 18:51 Pete L. Clark 44.7k

1

3

votes

1

answer

80

views

Compute the homology of the CW complex directly from the cell structure

algebraic-topology

apr 23 at 18:46 Pete L. Clark 44.7k

3

votes

1

answer

69

views

What do elements of the first homology group mean topologically?

general-topology algebraic-topology homology

apr 13 at 2:03 Mariano Suárez-Alvarez♦ 53.4k

1

3

votes

3

answers

203

views

What properties are allowed in comprehension axiom of ZFC?

set-theory axioms

jan 2 at 20:29 Dan Christensen 1,575

3

votes

2

answers

248

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Why is Taylor series expansion for $1/(1-x)$ valid only for $x \in (-1, 1)$?

power-series taylor-expansion

sep 23 at 18:55 Michael Hardy 48.4k

1

3

votes

2

answers

152

views

What is the name of the structure Z4 under subtraction?

group-theory universal-algebra

may 28 '12 at 20:00 user1729 3,354

2

votes

2

answers

36

views

Let $A$ be a set, $R$ an empty relation on $A$, what is $A/R$?

discrete-mathematics relations equivalence-relations

may 8 at 15:39 tomasz 7,200

2

votes

1

answer

62

views

What are the factors of $\aleph_0$?

elementary-set-theory cardinals infinity

apr 28 at 16:59 Michael Hardy 48.4k

2

votes

2

answers

60

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Given a topological space $X$, does $H_1(X)=\mathbb{Z}$ imply $\pi(X)=\mathbb{Z}$?

group-theory algebraic-topology

apr 25 at 5:40 Jyrki Lahtonen 31k

1

2

votes

2

answers

32

views

In Sets, describe the equalizer of the functions $f \circ p_1$ ,$ f \circ p_2 : A \times A → B$ as a (binary) relation on $A$

category-theory

apr 11 at 16:09 Clive Newstead 15.3k

1

2

votes

1

answer

61

views

Can boolean homomorphisms of boolean algebras correspond to ultrafilters?

abstract-algebra category-theory boolean-algebra

apr 3 at 16:04 Cameron Buie 27.7k

1

2

votes

2

answers

78

views

Why is an empty set not a terminal object in categories $\mathsf{Top}$ and $\mathsf{Sets}$?

category-theory

mar 27 at 18:47 David Toth 545

2

votes

1

answer

44

views

Given a represenation $\rho:G \to Gl(V)$ and a subrepresentation $W \subset V$, is $\rho_V(g) = \rho_W(g)?$

representation-theory

mar 7 at 14:25 Eric O. Korman 7,570

2

votes

3

answers

110

views

Correlation between polynomial equations and matrix determinants

linear-algebra matrices polynomials determinant

mar 3 at 17:10 Community♦ 1

1

2

votes

1

answer

66

views

Behaviour of deformation retraction of an unbounded interval to a point around t=1.

algebraic-topology dynamical-systems chaos-theory

feb 1 at 20:36 Stefan H. 1,856

2

votes

1

answer

63

views

Can we apply a successor operation in Peano's arithmetic infinitely many times, is the successor well defined?

definition axioms peano-axioms

jan 19 at 20:39 Community♦ 1

1

vote

1

answer

26

views

Torus interior homeomorphic to torus exterior

algebraic-topology

may 19 at 7:14 Grumpy Parsnip 9,589

1

vote

1

answer

43

views

Is $r:S^1 \to \{x_0\}$ a retraction?

algebraic-topology

may 7 at 4:53 Potato 8,811

1

vote

1

answer

35

views

Are there $CW$-complexes not homeomorphic to $\mathbb{R}P^2$ but homotopy equivalent to $\mathbb{R}P^2$ with at most $5$ cells?

algebraic-topology

may 2 at 5:30 Mariano Suárez-Alvarez♦ 53.4k

1

vote

1

answer

78

views

Does every continuous map induce a homomorphism on fundamental groups?

algebraic-topology

apr 30 at 9:44 user62163 66

1

vote

1

answer

36

views

What is $\phi(k)$ in $\sum_{k=1..n} \phi(k)\lfloor n/k \rfloor^2$?

sequences-and-series notation

aug 27 at 3:53 MJD 21.1k

1

vote

2

answers

139

views

What does the following notation mean: $\Bbb Q[x,y]$?

functions notation

aug 5 at 2:57 trb456 1,064

1

vote

0

answers

57

views

Is cycle index unique for every distinct group up to isomorphism?

group-theory

may 21 '12 at 8:50 David Toth 545

David Toth

29 Questions