Published online by Cambridge University Press: 15 March 2024
We prove an effective version of the Lopez-Escobar theorem for continuous domains. Let  $Mod(\tau )$ be the set of countable structures with universe
$Mod(\tau )$ be the set of countable structures with universe  $\omega $ in vocabulary
$\omega $ in vocabulary  $\tau $ topologized by the Scott topology. We show that an invariant set
$\tau $ topologized by the Scott topology. We show that an invariant set  $X\subseteq Mod(\tau )$ is
$X\subseteq Mod(\tau )$ is  $\Pi ^0_\alpha $ in the Borel hierarchy of this topology if and only if it is definable by a
$\Pi ^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 ^p_\alpha $-formula, a positive  $\Pi ^0_\alpha $ formula in the infinitary logic
$\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
$L_{\omega _1\omega }$. As a corollary of this result we obtain a new pullback theorem for positive computable embeddings: Let  $\mathcal {K}$ be positively computably embeddable in
$\mathcal {K}$ be positively computably embeddable in  $\mathcal {K}'$ by
$\mathcal {K}'$ by  $\Phi $, then for every
$\Phi $, then for every  $\Pi ^p_\alpha $ formula
$\Pi ^p_\alpha $ formula  $\xi $ in the vocabulary of
$\xi $ in the vocabulary of  $\mathcal {K}'$ there is a
$\mathcal {K}'$ there is a  $\Pi ^p_\alpha $ formula
$\Pi ^p_\alpha $ formula  $\xi ^{*}$ in the vocabulary of
$\xi ^{*}$ in the vocabulary of  $\mathcal {K}$ such that for all
$\mathcal {K}$ such that for all  $\mathcal {A}\in \mathcal {K}$,
$\mathcal {A}\in \mathcal {K}$,  $\mathcal {A}\models \xi ^{*}$ if and only if
$\mathcal {A}\models \xi ^{*}$ 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.
$\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.
 $\varSigma 01$
 and
$\varSigma 01$
 and 
 $\varPi 01$
equivalence structures
. 
Annals of Pure and Applied Logic
, vol. 162 (2011), no. 7, pp. 490–503.CrossRefGoogle Scholar
$\varPi 01$
equivalence structures
. 
Annals of Pure and Applied Logic
, vol. 162 (2011), no. 7, pp. 490–503.CrossRefGoogle Scholar $\varphi$
-spaces and applications
. 
Mathematical Logic Quarterly
, vol. 51 (2005), no. 1, pp. 45–61.CrossRefGoogle Scholar
$\varphi$
-spaces and applications
. 
Mathematical Logic Quarterly
, vol. 51 (2005), no. 1, pp. 45–61.CrossRefGoogle Scholar