Abstract
We show that the structure ℛ of recursively enumerable degrees is not a Σ₁-elementary substructure of 𝒟n, where 𝒟n (n>1) is the structure of n-r.e. degrees in the Ershov hierarchy.
Citation
Yue Yang. Liang Yu. "On Σ₁-structural differences among finite levels of the Ershov hierarchy." J. Symbolic Logic 71 (4) 1223 - 1236, December 2006. https://doi.org/10.2178/jsl/1164060453
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