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Sep
16
reviewed Leave Open How to compute $\lim_{n\rightarrow\infty}\frac1n\left\{(2n+1)(2n+2)\cdots(2n+n)\right\}^{1/n}$
Sep
16
reviewed No Action Needed Counting number of solutions for $x = (a-1)(b-2)(c-3)(d-4)(e-5)$
Sep
16
reviewed Approve Maximum of two positive operators
Sep
16
reviewed Looks OK What is the sum of this series?
Sep
14
reviewed Reviewed Prove that the field F is a vector space over itself.
Sep
14
reviewed Close $[E:F]$ can be divided by $|Gal(E/F)| $?
Sep
13
awarded  Good Answer
Sep
10
comment Proof for cyclic permutation
Write $a=(a_1,a_2,\dotsc,a_r)$, let $x$ be an element of $\{1,\dotsc,n\}$, and see what happens when you apply $a$ to $x$ $r$ times.
Sep
10
reviewed Approve Asymptotic bounds. What software to use?
Sep
10
comment Proving that 4 specified sets are not algebraic
For 3 and 4, assume $f$ is a polynomial vanishing on your specified set. Then by restricting to each line through the origin (i.e., set $y=\lambda x$ for some $\lambda$, or $x=0$), you can get a bunch of polynomials of one variable, each of which has infinitely many roots, so must be $0$. Thus you can show that $f$ vanishes everywhere. Possibly a similar method can be adapted to the others.
Sep
10
reviewed Close Twice as much vs Two times as much vs Double
Sep
10
reviewed Leave Open A map that is surjective but not injective between infinite dimensional vector spaces
Sep
10
reviewed Leave Open A form problem between $S^3$ and $S^2$.
Sep
10
reviewed Close A property of rings
Sep
10
reviewed Close A ring with few invertible elements
Sep
10
answered Show that $\operatorname{Hom}_R(M, -)$ is a functor from the category of $R$-modules to the category of abelian groups.
Sep
9
reviewed Reject Rational Points on Elliptic Curves
Sep
9
comment Canonical direct product (in a category)
It's also then true that such a choice of three pieces of information is unique up to unique isomorphism (once "isomorphism" is defined appropriately), so I'm not sure it's really necessary to single out one choice as canonical.
Sep
9
answered Simple Combinatorics Problem
Sep
9
comment Simple Combinatorics Problem
The question is a little unclear to me on whether one can tell the difference between each of the 5 letters. Concretely, in case 7, are there 5 possibilities depending on which letter is in the second box, or do you consider all of these equivalent?