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X-WR-CALDESC:évènements pour Département de mathématiques et applications
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TZID:Europe/Paris
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DTSTART:20130331T010000
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DTSTART:20131027T010000
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DTSTART;TZID=Europe/Paris:20131004T110000
DTEND;TZID=Europe/Paris:20131004T110000
DTSTAMP:20260405T174304
CREATED:20131004T090000Z
LAST-MODIFIED:20211104T094058Z
UID:8134-1380884400-1380884400@www.math.ens.psl.eu
SUMMARY:Church-Turing computability of the étale cohomology mod l
DESCRIPTION:[Work in common with Fabrice Orgogozo]The dimension of the étale cohomology groups\, with coefficients in Z/lZ\, of a scheme of finite type over an algebraically closed field of characteristic different from l\, is computable in the sense of Church-Turing. To prove this\, we construct a hypercovering of X by schemes (analogous to Artin’s ?Roegood neighborhoods?R) having algorithmically testable geometric properties which allow to reduce the computation of the cohomology of X to that of their completed fundamental group.
URL:https://www.math.ens.psl.eu/evenement/church-turing-computability-of-the-etale-cohomology-mod-l/
LOCATION:ENS salle W (escalier B 4è étage)
CATEGORIES:Séminaire Géométrie et théorie des modèles
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20131004T160000
DTEND;TZID=Europe/Paris:20131004T160000
DTSTAMP:20260405T174304
CREATED:20131004T140000Z
LAST-MODIFIED:20211104T094057Z
UID:8132-1380902400-1380902400@www.math.ens.psl.eu
SUMMARY:Tame definable topological dynamics
DESCRIPTION:(Joint work with Pierre Simon) I will present some new results on definably amenable groups in NIP theories (typical examples of which are definably amenable groups in o-minimal theories\, algebraically closed valued fields and p-adics). In particular I will demonstrate that in this context various notions of genericity coincide (answering some questions of Newelski and Petrykowski) and a characterization of ergodic measures will be given. Arguments rely on the theory of forking for types and measures in NIP theories and the so-called (p\,q)-theorem from combinatorics.If time permits\, I will describe how these results generalize to homogeneous spaces\, ind-definable groups and action of the group of automorphisms\, and how these developments can be viewed as a study of the definable case of abstract tame dynamical systems introduced by Glasner.
URL:https://www.math.ens.psl.eu/evenement/tame-definable-topological-dynamics/
LOCATION:ENS salle W (escalier B 4è étage)
CATEGORIES:Séminaire Géométrie et théorie des modèles
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