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Jun 15, 2020 at 7:27 history edited CommunityBot
Commonmark migration
Apr 5, 2016 at 10:48 answer added Johan timeline score: 3
Apr 1, 2016 at 22:14 answer added Alexander Braverman timeline score: 9
Apr 1, 2016 at 18:48 comment added Jason Starr For any (split) reductive group $G$ with maximal torus $T$ and Weyl group $\mathcal{W}$, Grothendieck proves that the set of $G$-torsors over $\mathbb{P}^1$ is naturally in bijection with the quotient of the cocharacter lattice of $T$, $\text{Hom}_{\textbf{GpSch}_k}(\mathbb{G}_{m,k},T)/\mathcal{W}$, where the $\mathcal{W}$-action is the natural action on $T$. Up to choosing a Weyl chamber of the cocharacter lattice, the specialization order should be something like adding the positive coroots.
Apr 1, 2016 at 18:33 comment added Jason Starr The theorem that you attribute to Grothendieck was first proved by Del Pezzo and Bertini (cf. the article of Harris on varieties of minimal degree). It was then rediscovered by Birkhoff. Grothendieck proved a vast generalization of this theorem. There is a beautiful article of Martens and Thaddeus on Grothendieck's theorem and its extensions.
Apr 1, 2016 at 18:26 history asked Qfwfq CC BY-SA 3.0