Geodesic
The branching theorem and computable categoricity in the Ershov hierarchy
Algebra i logika, Tome 54 (2015) no. 2, pp. 137-157

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Computable categoricity in the Ershov hierarchy is studied. We consider $F_a$- and $G_a$-categorical structures. These were introduced by B. Khoussainov, F. Stephan, and Y. Yang for $a$, which is a notation for a constructive ordinal. A generalization of the branching theorem is proved for $F_a$-categorical structures. As a consequence we obtain a description of $F_a$-categorical structures for classes of Boolean algebras and Abelian $p$-groups. Furthermore, it is shown that the branching theorem cannot be generalized to $G_a$-categorical structures.
Keywords: computable categoricity, Ershov hierarchy, $F_a$-categoricity, $G_a$-categoricity, branching structure. 
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     author = {N. A. Bazhenov},
     title = {The branching theorem and computable categoricity in the {Ershov} hierarchy},
     journal = {Algebra i logika},
     pages = {137--157},
     publisher = {mathdoc},
     volume = {54},
     number = {2},
     year = {2015},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2015_54_2_a0/}
}
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N. A. Bazhenov. The branching theorem and computable categoricity in the Ershov hierarchy. Algebra i logika, Tome 54 (2015) no. 2, pp. 137-157. http://geodesic.mathdoc.fr/item/AL_2015_54_2_a0/