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visits member for 4 years, 3 months
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umagon at google mail


Jan
4
reviewed Close $\alpha^{-1}(\ker(\beta))$, how to find?
Jan
4
reviewed Close Prove or disprove that the ideal $(2+4\mathbb{Z},x)$ is a principal ideal in $(\mathbb{Z}/4\mathbb{Z})[x]$
Jan
4
reviewed Close How to build a triangle
Jan
4
reviewed Close Krull dimension of quotients
Jan
4
comment Special Cases of Quadratic Reciprocity and Counting Fixed Points
Nice indeed! But it's not immediately clear how to generalize this: it's easy to find 3-torsion in $PSL_2(\mathbb Z)\cong\mathbb Z_2\ast\mathbb Z_3$ but not, say, 5-torsion...
Jan
4
reviewed Close math logic computer science
Jan
3
comment A combinatorial identity: $ \sum_{k=m}^n \frac{\binom{1/2}{k-m}}{k \binom{-1/2}{k}}=\frac{\binom{-1/2}{n-m}}{m \binom{-1/2}{n}} $
Looks amusing. What's the source?
Jan
3
revised Jacobi symbol $\left(\frac{(n+1)/2}{n}\right)$
descriptive title; tags
Jan
3
reviewed Reject suggested edit on Prove that there are no such different positive numbers that satisfy both $a+b=c+d$ and $a^3+b^3=c^3+d^3$.
Jan
3
reviewed Close About Saturation of Monomial Ideals
Jan
3
comment Show $\binom{n}{k}\binom{k}{a} = \binom{n}{a}\binom{n-a}{k-a}$ by block-walking interpretation of Pascal's triangle
Related: math.stackexchange.com/q/534202
Jan
3
reviewed Close The zero point problem of a function .
Jan
3
comment Is there anything to be learned from the spectrum of a cohomology ring?
AFAIK this POV is more useful in equivariant cohomology. For example, in the context of localization theorems it's natural (at least) to view $H_G(X)$ as a sheaf over $\operatorname{Spec}H_G(pt)$. See also Quillen. The Spectrum of an Equivariant Cohomology Ring and Goresky, MacPherson. On the Spectrum of the Equivariant Cohomology Ring...
Jan
3
comment Loop space and $K$-theory
possible duplicate of Yoneda's lemma and $K$-theory.
Jan
3
reviewed Close Why is $-a \times -b = ab$?
Jan
3
revised what does the “L” in “L-function” stand for?
ref. to the answer
Jan
3
reviewed Leave Open Prime factor of $2 \uparrow \uparrow 4 + 3\uparrow \uparrow 4$
Jan
3
revised If $x=123456789101112131415161718$, then $x\equiv 6\pmod{16}$ and $x\equiv 0\pmod 6$
edited tags; edited title
Jan
3
reviewed Close Show that the equation $x^3-3x+1=0$ has at least three solutions(Intermediate Value Theorem)
Jan
3
reviewed Close Prove $S_g$ retracts to $C$