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Leo
  • Member for 11 years, 3 months
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212 votes
10 answers
33k views

How do I sell out with abstract algebra?

141 votes
4 answers
7k views

Does $R[x] \cong S[x]$ imply $R \cong S$?

  • 3,675
79 votes
3 answers
9k views

Does every Abelian group admit a ring structure?

40 votes
4 answers
2k views

"Cayley's theorem" for Lie algebras?

27 votes
5 answers
2k views

Why does $(A/I)\otimes_R (B/J)\cong(A\otimes_R B)/(I\otimes_R 1+1\otimes_R J)$?

17 votes
2 answers
3k views

Hom and tensor with a flat module

  • 4,401
17 votes
1 answer
441 views

Does a finite ring's additive structure and the structure of its group of units determine its ring structure?

16 votes
2 answers
7k views

implicit equation for "double torus" (genus 2 orientable surface)

16 votes
2 answers
7k views

Is the localization of a PID a PID?

10 votes
3 answers
1k views

What are the limit points of $\tan(\mathbb{N})$ in $\mathbb{R}$?

  • 1,465
10 votes
2 answers
1k views

Can any smooth manifold be realized as the zero set of some polynomials?

7 votes
2 answers
485 views

Variety generated by finite fields

  • 6,857
7 votes
1 answer
1k views

How to compute the sum of every $k$-th binomial coefficient?

5 votes
2 answers
2k views

Showing that if $R$ is a commutative ring and $M$ an $R$-module, then $M \otimes_R (R/\mathfrak m) \cong M / \mathfrak m M$.

  • 4,495
4 votes
1 answer
288 views

Killing successive homotopy groups via fibrations

  • 6,857
3 votes
1 answer
399 views

$C \otimes A \cong C \otimes B$ does not imply $A \cong B$