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Displaying similar documents to “The Hurwitz action and braid group orderings.”

Presentations of étendues

Anders Kock, Ieke Moerdijk (1991)

Cahiers de Topologie et Géométrie Différentielle Catégoriques

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Classifying toposes and foliations

Ieke Moerdijk (1991)

Annales de l'institut Fourier

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For any etale topological groupoid G (for example, the holonomy groupoid of a foliation), it is shown that its classifying topos is homotopy equivalent to its classifying space. As an application, we prove that the fundamental group of Haefliger for the (leaf space of) a foliation agrees with the one introduced by Van Est. We also give a new proof of Segal’s theorem on Haefliger’s classifying space B Γ q .

Lie groupoids as generalized atlases

Jean Pradines (2004)

Open Mathematics

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Starting with some motivating examples (classical atlases for a manifold, space of leaves of a foliation, group orbits), we propose to view a Lie groupoid as a generalized atlas for the “virtual structure” of its orbit space, the equivalence between atlases being here the smooth Morita equivalence. This “structure” keeps memory of the isotropy groups and of the smoothness as well. To take the smoothness into account, we claim that we can go very far by retaining just a few formal properties...