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A LOPEZ-ESCOBAR THEOREM FOR CONTINUOUS DOMAINS

Published online by Cambridge University Press:  15 March 2024

NIKOLAY BAZHENOV
Affiliation:
SOBOLEV INSTITUTE OF MATHEMATICS NOVOSIBIRSK AND NOVOSIBIRSK STATE UNIVERSITY NOVOSIBIRSK, RUSSIA E-mail: bazhenov@math.nsc.ru
EKATERINA FOKINA
Affiliation:
INSTITUTE OF DISCRETE MATHEMATICS AND GEOMETRY TECHNISCHE UNIVERSITÄT WIEN VIENNA, AUSTRIA E-mail: ekaterina.fokina@tuwien.ac.at
DINO ROSSEGGER
Affiliation:
INSTITUTE OF DISCRETE MATHEMATICS AND GEOMETRY TECHNISCHE UNIVERSITÄT WIEN VIENNA, AUSTRIA E-mail: dino.rossegger@tuwien.ac.at
ALEXANDRA SOSKOVA
Affiliation:
FACULTY OF MATHEMATICS AND INFORMATICS SOFIA UNIVERSITY SOFIA, BULGARIA E-mail: asoskova@fmi.uni-sofia.bg
STEFAN VATEV*
Affiliation:
FACULTY OF MATHEMATICS AND INFORMATICS SOFIA UNIVERSITY SOFIA, BULGARIA

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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Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of The Association for Symbolic Logic

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