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Algebraic Geometer


Feb
10
awarded  Revival
Oct
21
awarded  Yearling
Sep
5
comment Is a pushout of a closed immersion $f$ again a closed immersion?
This seems relevant: mathoverflow.net/questions/29306/…
Feb
26
awarded  Revival
Oct
21
awarded  Yearling
Jul
27
awarded  Student
Jul
27
comment Solving a Laplacian in polar coordinates
@Thomas I see what you mean though, this is a problem.
Jul
27
comment Solving a Laplacian in polar coordinates
@Thomas According to the author of the book, there is no typo. I copied it correctly.
Jul
27
asked Solving a Laplacian in polar coordinates
May
31
comment quasi-finite maps to quasi-projective varieties?
@MattE Yes, I was working in the algebraic category.
May
27
answered Open properties of quasi-compact schemes
May
25
answered quasi-finite maps to quasi-projective varieties?
May
24
answered How to find a finite set of generators for $I \subset k[x_1, …, x_n]$
May
23
answered Geometric genus of a (possibly non-complete) intersection in P^n
May
5
comment Kähler differentials not the same as regular differentials on a singular curve
@Alan I'm guessing it has something to do with $y^2=x^3$ implying $2ydy=3x^2 dx$. Multiplying by $x$ gives $2xydy=3x^3 dx=3y^2 dy$ and dividing by $y$ gives $2xdy=3ydx$.
Apr
28
answered Varieties given by non-algebraic equations
Apr
27
comment Does this correctly show that the union of infinite affine varieties is not an affine variety?
Even a finite union of affine varieties is not necessarily affine, for instance projective space $\mathbb P^n= \bigcup_{i=0}^n U_i$ where $U_i \cong \mathbb A^n$. In fact, any positive dimensional projective variety is not affine and has a finite covering by open affine subsets.
Apr
27
comment How to find $\int{\left(\frac{\sqrt{x+1}}{x-1}\right)^x}dx$?
If this integral is from 2 to infinity, you can show it converges by using the integral test to make it into a series and then applying the root test. I think that's probably what they want you to do.
Apr
22
comment A nonsplit short exact sequence of abelian groups with $B \cong A \oplus C$
I should add that there is a 1-1 correspondence between elements of $Ext^1(C,A)$ and short exact sequences $0 \rightarrow A \rightarrow B \rightarrow C \rightarrow 0$ and this sequence splits iff it corresponds to the $0$ element of the Ext group.
Apr
22
answered A nonsplit short exact sequence of abelian groups with $B \cong A \oplus C$