Introduction to Wild Ramification of Schemes and Sheaves
نویسنده
چکیده
1. Brief summary onétale cohomology In this section, k denotes a field, a scheme will mean a separated scheme of finite type over k and a morphism of schemes will mean a morphism over k. We put p = char k. 1.1. Definition and examples ofétale sheaves. A morphism X → Y of schemes is said to bé etale if Ω 1 X/Y = 0 and if X is flat over Y. Example 1.1. An open immersion isétale. The morphism G m = Spec k[T ±1 ] → G m defined by T → T m isétale if and only if m is invertible in k. The morphism G a = Spec k[T ] → G a defined by T → T p − T isétale if p > 0.
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Wild ramification of schemes and sheaves
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