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Published online by Cambridge University Press: 22 November 2021
For a ring R, Hilbert’s Tenth Problem $HTP(R)$ is the set of polynomial equations over R, in several variables, with solutions in R. We view
$HTP$ as an enumeration operator, mapping each set W of prime numbers to
$HTP(\mathbb {Z}[W^{-1}])$, which is naturally viewed as a set of polynomials in
$\mathbb {Z}[X_1,X_2,\ldots ]$. It is known that for almost all W, the jump
$W'$ does not
$1$-reduce to
$HTP(R_W)$. In contrast, we show that every Turing degree contains a set W for which such a
$1$-reduction does hold: these W are said to be HTP-complete. Continuing, we derive additional results regarding the impossibility that a decision procedure for
$W'$ from
$HTP(\mathbb {Z}[W^{-1}])$ can succeed uniformly on a set of measure
$1$, and regarding the consequences for the boundary sets of the
$HTP$ operator in case
$\mathbb {Z}$ has an existential definition in
$\mathbb {Q}$.