Заглавие | DEGREE SPECTRA AND CO-SPECTRA OF STRUCTURES |
Вид публикация | Journal Article |
Година на публикуване | 2004 |
Автори | Soskov I |
Списание | Annuaire de l’Université de Sofia “St. Kliment Ohridski”. Faculté de Mathématiques et Informatique |
Том | 96 |
ключови думи | degree spectra, enumeration degrees |
Резюме | Given a countable structure $\mathfrak{A}$, we define the degree spectrum $DS(\mathfrak{A})$ of $\mathfrak{A}$ to be the set of all enumeration degrees generated by the presentations of $\mathfrak{A}$ on the natural numbers. The co-spectrum of $\mathfrak{A}$ is the set of all lower bounds of $DS(\mathfrak{A})$. We prove some general properties of the degree spectra, which show that they behave with respect to their co-spectra very much like the cones of enumeration degrees. Among the results are the analogs of Selman's Theorem [14], the Minimal Pair Theorem and the existence of a quasi-minimal enumeration degree. |
2000 MSC | 03D45, 03D30 |
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0596.pdf | 28 KB |
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96-045-068.pdf | 2.07 MB |