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Singularities in algebraic/complex/differential geometry and analysis of ODEs/PDEs. Singular spaces, vector fields, etc.

6 votes
1 answer
1k views

Blowing-up an ordinary double point, then contracting the exceptional locus to a curve

Let $X\subset\mathbb P^4$ a projective hypersurface with an ordinary double point at $o\in X$. Blow-up $\mathbb P^4$ at $o$ and let $E\simeq\mathbb P^3$ the exceptional divisor of this blow-up. Consi …
diverietti's user avatar
  • 7,902
28 votes
Accepted

construct the elliptic fibration of elliptic k3 surface

Let $S$ be a smooth projective $K3$ surface, say over the complex numbers, and suppose that $S$ admits a (non-constant) fibration $\pi\colon S\to C$ over a curve $C$. By the universal property of th …
diverietti's user avatar
  • 7,902
32 votes
Accepted

Elementary short exact sequence of sheaves

Expanding the comment of Donu Arapura, let $X$ be a variety and $Y\subset X$ a subvariety. Then, you have a short exact sequence of sheaves $$ 0\to\mathcal I_Y\to\mathcal O_X\to\mathcal O_X/\mathcal I …
diverietti's user avatar
  • 7,902