## Extension d’une valuation

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**359**(2007), 3439-3481 Request permission

## Abstract:

We want to determine all the extensions of a valuation $\nu$ of a field $K$ to a cyclic extension $L$ of $K$, i.e. $L=K(x)$ is the field of rational functions of $x$ or $L=K(\theta )$ is the finite separable extension generated by a root $\theta$ of an irreducible polynomial $G(x)$. In two articles from 1936, Saunders MacLane has introduced the notions of*key polynomial*and of

*augmented valuation*for a given valuation $\mu$ of $K[x]$, and has shown how we can recover any extension to $L$ of a discrete rank one valuation $\nu$ of $K$ by a countable sequence of augmented valuations $\bigl (\mu _i\bigr ) _{i \in I}$, with $I \subset \mathbb N$. The valuation $\mu _i$ is defined by induction from the valuation $\mu _{i-1}$, from a key polynomial $\phi _i$ and from the value $\gamma _i = \mu ( \phi _i )$. In this article we study some properties of the augmented valuations and we generalize the results of MacLane to the case of any valuation $\nu$ of $K$. For this we need to introduce

*simple admissible families*of augmented valuations ${\mathcal A} = \bigl ( \mu _{\alpha } \bigr ) _{\alpha \in A}$, where $A$ is not necessarily a countable set, and to define a

*limit key polynomial*and

*limit augmented valuation*for such families. Then, any extension $\mu$ to $L$ of a valuation $\nu$ on $K$ is again a limit of a family of augmented valuations. We also get a “factorization” theorem which gives a description of the values $( \mu _{\alpha } (f))$ for any polynomial $f$ in $K[x]$.

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## Additional Information

**Michel Vaquié**- Affiliation: Laboratoire Émile Picard, UMR 5580, Université Paul Sabatier, UFR MIG, 31062 Toulouse Cedex 9, France
- Email: vaquie@math.ups-tlse.fr
- Received by editor(s): March 29, 2004
- Received by editor(s) in revised form: July 18, 2005
- Published electronically: February 12, 2007
- © Copyright 2007 American Mathematical Society
- Journal: Trans. Amer. Math. Soc.
**359**(2007), 3439-3481 - MSC (2000): Primary 13A18; Secondary 12J10, 14E15
- DOI: https://doi.org/10.1090/S0002-9947-07-04184-0
- MathSciNet review: 2299463