Wednesday, 6 January 2010

nt.number theory - Decomposition of primes, where the residue field extensions are allowed to be inseparable

I've been dealing with the following situation:



Let RsubseteqS be an extension of Dedekind rings, where Quot(R)=:LsubseteqE:=Quot(S) is a G-Galois extension. Let mathfrakp be a prime of R, and mathfrakq a primes of S above mathfrakp. Let Dmathfrakq denote the decomposition group, and Imathfrakq the inertia group, of mathfrakq over mathfrakp.



However, unlike in the classic case, I allow the residue fields of mathfrakp to be infinite, with positive characteristic. So the extension of residue fields may be inseparable.



It seems that the paper I'm reading implicitly assumes:



|Imathfrakq|=e[kappa(mathfrakq):kappa(mathfrakp)]i (the ramification index times the inseparability degree of the residue extension)


|Dmathfrakq|=e[kappa(mathfrakq):kappa(mathfrakp)]


|G|=re[kappa(mathfrakq):kappa(mathfrakp)] (where r is the number of primes above mathfrakp)



Is that right? I keep hitting walls when I try to prove it.

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