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A valuation theoretic characterization of recursively saturated real closed fields

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 Added by Salma Kuhlmann
 Publication date 2012
  fields
and research's language is English




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We give a valuation theoretic characterization for a real closed field to be recursively saturated. Our result extends the characterization of Harnik and Ressayre cite{hr} for a divisible ordered abelian group to be recursively saturated.



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In an extended abstract Ressayre considered real closed exponential fields and integer parts that respect the exponential function. He outlined a proof that every real closed exponential field has an exponential integer part. In the present paper, we give a detailed account of Ressayres construction, which becomes canonical once we fix the real closed exponential field, a residue field section, and a well ordering of the field. The procedure is constructible over these objects; each step looks effective, but may require many steps. We produce an example of an exponential field $R$ with a residue field $k$ and a well ordering $<$ such that $D^c(R)$ is low and $k$ and $<$ are $Delta^0_3$, and Ressayres construction cannot be completed in $L_{omega_1^{CK}}$.
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