Research output: Contribution to journal › Article › peer-review
Jump inversions of algebraic structures and Σ-definability. / Faizrahmanov, Marat; Kach, Asher; Kalimullin, Iskander et al.
In: Mathematical Logic Quarterly, Vol. 65, No. 1, 01.05.2019, p. 37-45.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Jump inversions of algebraic structures and Σ-definability
AU - Faizrahmanov, Marat
AU - Kach, Asher
AU - Kalimullin, Iskander
AU - Montalbán, Antonio
AU - Puzarenko, Vadim
N1 - Publisher Copyright: © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
PY - 2019/5/1
Y1 - 2019/5/1
N2 - It is proved that for every countable structure A and a computable successor ordinal α there is a countable structure A−α which is (Formula presented.) -least among all countable structures C such that A is Σ-definable in the αth jump C(α). We also show that this result does not hold for the limit ordinal α = ω. Moreover, we prove that there is no countable structure A with the degree spectrum (Formula presented.) for (Formula presented.).
AB - It is proved that for every countable structure A and a computable successor ordinal α there is a countable structure A−α which is (Formula presented.) -least among all countable structures C such that A is Σ-definable in the αth jump C(α). We also show that this result does not hold for the limit ordinal α = ω. Moreover, we prove that there is no countable structure A with the degree spectrum (Formula presented.) for (Formula presented.).
KW - THEOREM
KW - REDUCIBILITY
UR - http://www.scopus.com/inward/record.url?scp=85065422390&partnerID=8YFLogxK
U2 - 10.1002/malq.201800015
DO - 10.1002/malq.201800015
M3 - Article
AN - SCOPUS:85065422390
VL - 65
SP - 37
EP - 45
JO - Mathematical Logic Quarterly
JF - Mathematical Logic Quarterly
SN - 0942-5616
IS - 1
ER -
ID: 20039318