Abstract

A chain-closed field is defined as a chainable field which does not admit any "faithful" algebraic extension, and can also be seen as a field having a Henselian valuation $\nu$ such that the residue field $K/\nu$ is real closed and the value group $\nu K$ is odd divisible with $|\nu K/2\nu K| = 2$. If $K$ admits only one such valuation, we show that $f \in K$ is in $\mathbf{\Sigma} K^{2n} \operatorname{iff}$ for any real algebraic extension $L$ of $K, "f \subseteq \mathbf{\Sigma}L^{2n}"$ holds. The conclusion is also true for $K = \mathbf{R})$, and in the case $n = 1$ it holds for several variables and any real field $K$.