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Published online by Cambridge University Press: 20 November 2018
We search for theorems that, given a ${{C}_{i}}$-field
$K$ and a subfield
$k$ of
$K$, allow us to conclude that
$k$ is a
${{C}_{j}}$ -field for some
$j$. We give appropriate theorems in the case
$\text{case }K=k\left( t \right)$ and
$K=k\left( \left( t \right) \right)$. We then consider the more difficult case where
$K/k$ is an algebraic extension. Here we are able to prove some results, and make conjectures. We also point out the connection between these questions and Lang's conjecture on nonreal function fields over a real closed field.