Juan S

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4,665 reputation

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	seen	May 14 at 3:14
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11 Favorites

added views newest activity votes

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kviews

$n!$ is never a perfect square if $n\geq2$. Is there a proof of this that doesn't use Chebyshev's theorem?

number-theory factorial alternative-proof

jan 31 '12 at 20:46 Srivatsan 15.6k

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25

votes

1

answer

1

kviews

Sheaf cohomology: what is it and where can I learn it?

reference-request algebraic-topology algebraic-geometry soft-question sheaf-theory

jul 31 '11 at 15:55 Akhil Mathew 16.2k

10

25

votes

2

answers

402

views

When is the product of $n$ subgroups a subgroup?

abstract-algebra group-theory

sep 8 at 22:37 Hagen von Eitzen 42.4k

1

16

votes

1

answer

224

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Does every continuous map from $\mathbb{H}P^{2n+1}$ to itself have a fixed point?

general-topology algebraic-topology fixed-point-theorems

feb 4 '12 at 23:55 Matthew Pancia 172

2

15

votes

2

answers

389

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Why is $f(x) = x\phi(x)$ one-to-one?

number-theory totient-function

sep 28 '11 at 4:52 jspecter 5,712

6

11

votes

1

answer

331

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Why isn't $H^*(\mathbb{R}P^\infty,\mathbb{F}_2)\cong \mathbb{F}_2[[x]]$?

algebraic-topology cohomology

feb 21 '12 at 1:38 Juan S 4,665

6

11

votes

2

answers

275

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For every $k \in {\mathbb Z}$ construct a continuous map $f: S^n \to S^n$ with $\deg(f) = k$.

homework algebraic-topology

feb 28 '12 at 11:14 Asaf Karagila 90.9k

2

8

votes

1

answer

117

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Group structure on $\mathbb R P^n$

algebraic-topology topological-groups

jun 21 '12 at 23:44 Juan S 4,665

4

8

votes

2

answers

247

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Universal property of free module, “converse”

abstract-algebra modules

oct 22 at 23:38 Brian M. Scott 154k

2

8

votes

2

answers

104

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Homology of the fiber of a fibration

algebraic-topology spectral-sequences

feb 14 at 1:31 Mariano Suárez-Alvarez♦ 53.2k

1

2

votes

4

answers

103

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What is the possibility of choosing three balls in a certain sequence given a certain number of attempts?

probability

oct 2 at 16:20 Marc van Leeuwen 23.9k

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