Recursive expansions
Fundamenta Mathematicae, Tome 145 (1994) no. 2, pp. 153-169
Cet article a éte moissonné depuis la source Institute of Mathematics Polish Academy of Sciences
Let A be a recursive structure, and let ψ be a recursive infinitary ${Π}_2$ sentence involving a new relation symbol. The main result of the paper gives syntactical conditions which are necessary and sufficient for every recursive copy of A to have a recursive expansion to a model of ψ, provided A satisfies certain decidability conditions. The decidability conditions involve a notion of rank. The main result is applied to prove some earlier results of Metakides-Nerode and Goncharov. In these applications, the ranks turn out to be low, but there are examples in which the rank takes arbitrary recursive ordinal values.
@article{10_4064_fm_145_2_153_169,
author = {C. Ash and J. Knight},
title = {Recursive expansions},
journal = {Fundamenta Mathematicae},
pages = {153--169},
year = {1994},
volume = {145},
number = {2},
doi = {10.4064/fm-145-2-153-169},
language = {en},
url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-145-2-153-169/}
}
C. Ash; J. Knight. Recursive expansions. Fundamenta Mathematicae, Tome 145 (1994) no. 2, pp. 153-169. doi: 10.4064/fm-145-2-153-169
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