Published online by Cambridge University Press: 20 November 2018
A preordering $T$ is constructed in the polynomial ring
$A=\mathbb{R}[{{t}_{1}},{{t}_{2}},...]$ (countablymany variables) with the following two properties: (1) For each
$f\,\in \,A$ there exists an integer
$N$ such that
$-\,N\,\le \,f\left( p \right)\,\le \,N$
holds for all
$P\in \text{Spe}{{\text{r}}_{T}}(A)$. (2) For all
$f\,\in \,A$, if
$N+f,N-f\in T$ for some integer
$N$, then
$f\,\in \,\mathbb{R}$. This is in sharp contrast with the Schmüdgen-Wörmann result that for any preordering
$T$ in a finitely generated
$\mathbb{R}$-algebra
$A$, if property (1) holds, then for any
$f\in A,f>0\,\text{on}\,\text{Spe}{{\text{r}}_{T}}(A)\Rightarrow f\in T$. Also, adjoining to
$A$ the square roots of the generators of
$T$ yields a larger ring
$C$ with these same two properties but with
$\sum{{{C}^{2}}}$ (the set of sums of squares) as the preordering.