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Birationality of étale maps via surgery

  • Scott Nollet , Laurence R. Taylor and Frederico Xavier
Published/Copyright: January 8, 2009
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Journal für die reine und angewandte Mathematik
From the journal Volume 2009 Issue 627

Abstract

We use a counting argument and surgery theory to show that if D is a sufficiently general algebraic hypersurface in , then any local diffeomorphism F : X of simply connected manifolds which is a d-sheeted cover away from D has degree d = 1 or d = ∞ (however all degrees d > 1 are possible if F fails to be a local diffeomorphism at even a single point). In particular, any étale morphism F : X of algebraic varieties which covers away from such a hypersurface D must be birational.

Received: 2007-04-26
Revised: 2007-10-07
Published Online: 2009-01-08
Published in Print: 2009-February

© Walter de Gruyter Berlin · New York 2009

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