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arXiv · 1301.1940

On the Langlands retraction

Vladimir Drinfeld
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Abstract

Given a root system in a vector space V, Robert Langlands defined in 1973 a canonical retraction of V onto the dominant chamber. In this note we give a short review of the material on this retraction (which is well known under the name of "Langlands' geometric lemmas"). The main purpose of this review is to provide a convenient reference for e-print arXiv:1112.2402 by D.Gaitsgory and me, in which the Langlands retraction is used to define a certain coarsening of the Harder-Narasimhan-Shatz stratification of the stack of G-bundles on a smooth projective curve.

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Vladimir Drinfeld. 2013-01-09. On the Langlands retraction. https://arxiv.org/abs/1301.1940

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