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benblumsmith
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21 votes
4 answers
3k views

Using a known result without a specific reference

21 votes
2 answers
1k views

Direct combinatorial proof that $2^{2k} = \sum \binom{2i}{i}\binom{2j}{j}$?

17 votes
2 answers
593 views

When can a finite subgroup of $GL(2n,\mathbb{R})$ be viewed as a subgroup of $GL(n,\mathbb{C})$?

12 votes
1 answer
619 views

How bad does a ring have to be for a failure of "going-in-between"?

11 votes
2 answers
820 views

Sums of subsets of $\mathbb{Z}/n\mathbb{Z}$

10 votes
1 answer
1k views

Explicit isomorphism for quaternion algebras over $\mathbb{Q}$?

10 votes
2 answers
442 views

Quotient of $S^3$ by Montgomery and Zippin's "wild involution"

9 votes
3 answers
406 views

How do small central extensions drop the dimension of a faithful representation?

9 votes
2 answers
602 views

Smallest faithful matrix representation of the exterior algebra

8 votes
1 answer
382 views

Are all real-closed subfields of $\overline{\mathbb{Q}}$ conjugate?

8 votes
1 answer
330 views

How fine an invariant of a representation is its quotient singularity?

8 votes
1 answer
233 views

Is the restriction of a graded automorphism linearizable in characteristic zero?

7 votes
0 answers
287 views

Hironaka decomposition over $\mathbb{Z}$?

7 votes
1 answer
336 views

Does the Fano plane "embed" in the complex projective plane?

7 votes
1 answer
414 views

Does the strict henselization satisfy Going-Up?

6 votes
0 answers
115 views

What are Burnside's "fixed systems" in modern language?

6 votes
0 answers
179 views

Quotients of 4-sphere by smooth $Z_p$ actions with knotted fixed point sets

6 votes
1 answer
419 views

History of name "Fundamental Theorem on Symmetric Polynomials"

6 votes
1 answer
280 views

Quotient of Coxeter complex in terms of double cosets?

5 votes
2 answers
325 views

Embedding $G$ in a $Z(G)$ extension of $\operatorname{Aut}G$

5 votes
1 answer
208 views

If a finite poset supports a Cohen-Macaulay ASL, how far can it be from Cohen-Macaulay?

5 votes
1 answer
325 views

Do monotone functions on the interval have an "Alexander duality" property?

5 votes
1 answer
246 views

What does Rosenlicht mean by a "point"? By $k(v_1,v_2)$?

4 votes
1 answer
334 views

Why do Nakajima and Watanabe claim the induced action of a finite linear group on the invariant subring of the reflection subgroup is linearizable?

4 votes
1 answer
139 views

Given finite $G\subset O(n)$, is there a "standard" cell structure on $S^{n-1}$ with $G$ acting cellularly?

3 votes
2 answers
427 views

Paper of Denis Simon on quadratic equations in dimensions 4, 5?

3 votes
2 answers
285 views

Character kernels in the lattice of subgroups of a finite abelian group

3 votes
1 answer
249 views

Is the restriction of a graded automorphism of a polynomial ring to a polynomial subring linearizeable?

2 votes
1 answer
186 views

Relation between Riemannian and Cayley-graph distance in a finite Coxeter group