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 Yearling
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Feb
2
answered Prove that all automorphisms of the line $\Bbb A^1$ are of the form $f(x) = ax + b$ with $a\neq 0$.
Jan
25
answered Find a nontrivial proper ideal of $\mathbb{Z}\times\mathbb{Z}$ that is not prime
Jan
22
awarded  Yearling
Jan
11
comment Significance of various lex sort on polynomials
This is pretty well described in "Ideals, Varieties and Algorithms" by Cox, Little and O'Shea.
Dec
29
comment The definition of syzygies - free or projective?
For your last sentence: over a local ring, every projective module is free.
Dec
10
comment Bound of polynomial of degree n with Euclidean norms
It is not possible to solve this as stated, as existence of such positive $c_1$ would imply that the only zero of $p$ is for $x = 0$. You probably need to reformulate it somehow.
Nov
27
comment Smallest topology making projections continuous
Show that any topology that makes projections continuous must contain a basis of Euclidean topology, so it may not be any smaller than Euclidean topology.
Aug
18
comment Why sigma notation?
A tradition, probably. I don't think that there's any better reason. The sigma notation is older than bigcup notation.
Aug
18
answered Why is the Apollonian Gasket composed of infinitely many circles?
Aug
18
comment Abelian group and their subgroups
Let A be a given abelian group, G be a subgroup of order $m$, and H a subgroup of order $n$. Consider a subgroup $B$ of $A$ generated by the union $G \cup H$. It's finite, because $A$ is abelian, and has $G$ and $H$ as subgroups. It's enough then to prove it for the case of $A$ finite. There's a clear description of finite abelian group, and the solution of your problem stems pretty quickly from that.
Aug
15
answered Is there a name for the operation which is the union of two sets, but keeps duplicates?
Jul
16
answered The local ring of the generic point of a prime divisor
Jul
16
answered Combine 2 vector spaces commutatively
May
14
answered How to prove this limit is equal to $\beta/a$?
May
13
comment What is the least positive integer $m$ such that $\text{rank} A^m=\text{rank} A^{m+1}$?
Could you clarify what is $A$?
May
13
comment Integral of matrices
Is there anything else known about $\kappa$? Is it maybe orthogonal by any chance?
May
13
answered Are cardinal numbers sets in ZFC?
Mar
16
answered sufficient condition for varieties to meet transversally
Jan
22
awarded  Yearling
Dec
19
comment Image of open set is not open?
I wouldn't say that there's any duality between preimage and image. For one thing, the preimage of the intersection is the intersection of the preimages, but the image of the intersection is not the intersection of the images.