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Melle Hernández, Alejandro and Wall, Charles Terence Clegg
(2001)
*Pencils of curves on smooth surfaces.*
Proceedings of the London Mathematical Society , 83
(2 ).
257-278 .
ISSN 0024-6115

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Official URL: http://plms.oxfordjournals.org/

## Abstract

Although the theory of singularities of curves - resolution, classification, numerical invariants - goes through with comparatively little change in finite characteristic, pencils of curves are more difficult. Bertini's theorem only holds in a much weaker form, and it is convenient to restrict to pencils such that, when all base points are resolved, the general member of the pencil becomes non-singular. Even here, the usual rule for calculating the Euler characteristic of the resolved surface has to be modified by a term measuring wild ramification.

We begin by describing this background, then proceed to discuss the exceptional members of a pencil. In characteristic 0 it was shown by Há and Lê and by Lê and Weber, using topological reasoning, that exceptional members can be characterised by their Euler characteristics. We present a combinatorial argument giving a corresponding result in characteristic p. We first treat pencils with no base points, and then reduce the remaining case to this.

Item Type: | Article |
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Uncontrolled Keywords: | Numerical invariants of singularities; Characteristic p; Singularities of curves; Resolution; Bertini’s theorem; Pencil; Euler characteristic; Wild ramification |

Subjects: | Sciences > Mathematics > Algebraic geometry |

ID Code: | 13210 |

Deposited On: | 06 Sep 2011 07:53 |

Last Modified: | 06 Feb 2014 09:43 |

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