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 Mar28 awarded Necromancer Oct21 awarded Yearling Sep24 awarded Autobiographer Feb10 awarded Revival Oct21 awarded Yearling Sep5 comment Is a pushout of a closed immersion $f$ again a closed immersion? This seems relevant: mathoverflow.net/questions/29306/… Feb26 awarded Revival Oct21 awarded Yearling Jul27 awarded Student Jul27 comment Solving a Laplacian in polar coordinates @Thomas I see what you mean though, this is a problem. Jul27 comment Solving a Laplacian in polar coordinates @Thomas According to the author of the book, there is no typo. I copied it correctly. Jul27 asked Solving a Laplacian in polar coordinates May31 comment quasi-finite maps to quasi-projective varieties? @MattE Yes, I was working in the algebraic category. May27 answered Open properties of quasi-compact schemes May25 answered quasi-finite maps to quasi-projective varieties? May24 answered How to find a finite set of generators for $I \subset k[x_1, …, x_n]$ May23 answered Geometric genus of a (possibly non-complete) intersection in P^n May5 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 $2xdy=3ydx$. Apr28 answered Varieties given by non-algebraic equations Apr27 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.