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Algebra i logika, 2012, Volume 51, Number 4, Pages 423–428 (Mi al544)  

$\Delta^0_2$-poset with no positive presentation

J. Wallbaum
References:
Abstract: S. Yu. Podzorov in [Mat. Trudy, 9, No. 2, 109–132 (2006)] proved the validity of the following
THEOREM. If $\langle L,\le_L\rangle$ is a local lattice and $v$ a numbering of $L$ such that the relation $v(x)\le_L v(y)$ is $\Delta^0_2$-computable, then there is a numbering $\mu$ of $L$ such that the relation $\mu(x)\le_L\mu(y)$ is computably enumerable.
Podzorov also asked whether the hypothesis that $\langle L,\le_L\rangle$ is a local lattice is needed or the theorem is true of any partially ordered set (poset). We answer his question by constructing a poset for which the theorem fails.
Keywords: partially ordered set, local lattice, computably enumerable set.
Received: 28.04.2010
English version:
Algebra and Logic, 2012, Volume 51, Issue 4, Pages 281–284
DOI: https://doi.org/10.1007/s10469-012-9191-8
Bibliographic databases:
Document Type: Article
UDC: 510.5
Language: Russian
Citation: J. Wallbaum, “A $\Delta^0_2$-poset with no positive presentation”, Algebra Logika, 51:4 (2012), 423–428; Algebra and Logic, 51:4 (2012), 281–284
Citation in format AMSBIB
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\paper A~$\Delta^0_2$-poset with no positive presentation
\jour Algebra Logika
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\vol 51
\issue 4
\pages 423--428
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\jour Algebra and Logic
\yr 2012
\vol 51
\issue 4
\pages 281--284
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    Алгебра и логика Algebra and Logic
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