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A LOPEZ-ESCOBAR THEOREM FOR CONTINUOUS DOMAINS
Published online by Cambridge University Press: 15 March 2024
Abstract
We prove an effective version of the Lopez-Escobar theorem for continuous domains. Let $Mod(\tau )$ be the set of countable structures with universe
$\omega $ in vocabulary
$\tau $ topologized by the Scott topology. We show that an invariant set
$X\subseteq Mod(\tau )$ is
$\Pi ^0_\alpha $ in the Borel hierarchy of this topology if and only if it is definable by a
$\Pi ^p_\alpha $-formula, a positive
$\Pi ^0_\alpha $ formula in the infinitary logic
$L_{\omega _1\omega }$. As a corollary of this result we obtain a new pullback theorem for positive computable embeddings: Let
$\mathcal {K}$ be positively computably embeddable in
$\mathcal {K}'$ by
$\Phi $, then for every
$\Pi ^p_\alpha $ formula
$\xi $ in the vocabulary of
$\mathcal {K}'$ there is a
$\Pi ^p_\alpha $ formula
$\xi ^{*}$ in the vocabulary of
$\mathcal {K}$ such that for all
$\mathcal {A}\in \mathcal {K}$,
$\mathcal {A}\models \xi ^{*}$ if and only if
$\Phi (\mathcal {A})\models \xi $. We use this to obtain new results on the possibility of positive computable embeddings into the class of linear orderings.
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- © The Author(s), 2024. Published by Cambridge University Press on behalf of The Association for Symbolic Logic
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