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Fields of characteristic $p$, i.e., fields for which there is a prime $p$ such that $px=0$ for each $x$. Do not use this tag for questions on characteristic polynomials of a matrix.

9 votes
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Smoothness of hyperplane sections

Spread out $X$ over some $R=\mathbf{Z}[1/n]$ to a hypersurface $\mathcal{X} \subseteq \mathbf{P}^n_R$ that is smooth and projective over $R$. The standard proof of the Bertini smoothness theorem (as …
Bjorn Poonen's user avatar
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17 votes
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Are automorphism groups of hypersurfaces reduced ?

If $X$ is a smooth hypersurface in $\mathbf{P}^{n+1}$ of degree $d$, where $n \ge 1$, $d \ge 3$, and $(n,d) \ne (1,3)$, then $H^0(X,T_X)=0$ by Theorem 11.5.2 in Katz and Sarnak, Random matrices, Frobe …
Bjorn Poonen's user avatar
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