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 Algebra Logika: Year: Volume: Issue: Page: Find

 Algebra Logika, 2015, Volume 54, Number 2, Pages 212–235 (Mi al688)

Preserving categoricity and complexity of relations

J. Johnsona, J. F. Knightb, V. Ocasioc, J. Tussupovd, S. VanDenDriesschee

a Dept. of Math., Westfield State Univ., 577 Western Ave, Westfield, MA, 01086-1630, USA
b Dep. Math., Univ. Notre Dame, 255 Hurley, Notre Dame, IN, 46556, USA
c Dept. of Math. Sci., Univ. of Puerto Rico, PO Box 9000, Mayaguez, PR 00681-9000, USA
d Gumilyov Eurasian National University, ul. Satpaeva 2, Astana, Kazakhstan
e First Source Bank, South Bend, Indiana, USA

Abstract: In [Algebra i Logika, 16, No. 3 (1977), 257–282; Ann. Pure Appl. Logic, 136, No. 3 (2005), 219–246; J. Symb. Log., 74, No. 3 (2009), 1047–1060], it was proved that for each computable ordinal $\alpha$, there is a structure that is $\Delta^0_\alpha$ categorical but not relatively $\Delta^0_\alpha$ categorical. The original examples were not familiar algebraic kinds of structures. In [Ann. Pure Appl. Logic, 115, Nos. 1–3 (2002), 71–113], it was shown that for $\alpha=1$, there are further examples in several familiar classes of structures, including rings and $2$-step nilpotent groups. Similar examples for all computable successor ordinals were constructed in [Algebra i Logika, 46, No. 4 (2007), 514–524]. In the present paper, this result is extended to computable limit ordinals. We know of an example of an algebraic field that is computably categorical but not relatively computably categorical. Here we show that for each computable limit ordinal $\alpha>\omega$, there is a field which is $\Delta^0_\alpha$ categorical but not relatively $\Delta^0_\alpha$ categorical. Examples on dimension and complexity of relations are given.

Keywords: $\Delta^0_\alpha$ categorical structure, structure that is not relatively $\Delta^0_\alpha$categorical, field.

DOI: https://doi.org/10.17377/alglog.2015.54.205

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English version:
Algebra and Logic, 2015, 54:2, 140–154

Bibliographic databases:

UDC: 510.5

Citation: J. Johnson, J. F. Knight, V. Ocasio, J. Tussupov, S. VanDenDriessche, “Preserving categoricity and complexity of relations”, Algebra Logika, 54:2 (2015), 212–235; Algebra and Logic, 54:2 (2015), 140–154

Citation in format AMSBIB
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