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 Yearling
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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.
Nov
10
comment Find a subsheaf of a coherent sheaf, whose quotient is torsion sheaf.
Use induction on $r$.
Oct
30
awarded  Benefactor
Oct
30
accepted Global generation of $\mathcal{O}_{\mathbb{P}(\mathcal{E})}(1)$ and $\mathcal{E}$
Aug
1
comment What are differences between affine space and vector space?
What is it precisely that you need explained?
Jul
2
awarded  Curious
Jun
19
comment Showing holomorphic function is constant via conformal map
en.wikipedia.org/wiki/Joukowsky_transform
Jun
19
asked properties of certain semigroup action on $\mathbb{Z}/p\mathbb{Z}$