Аннотация
Computably enumerable equivalence relations (ceers) received a lot of attention in the literature. The standard tool to classify ceers is provided by the computable reducibility ⩽ c. This gives rise to a rich degree structure. In this paper, we lift the study of c-degrees to the Δ20 case. In doing so, we rely on the Ershov hierarchy. For any notation a for a non-zero computable ordinal, we prove several algebraic properties of the degree structure induced by ⩽ c on the Σa-1\Πa-1 equivalence relations. A special focus of our work is on the (non)existence of infima and suprema of c-degrees.
Язык оригинала | английский |
---|---|
Страницы (с-по) | 835-864 |
Число страниц | 30 |
Журнал | Archive for Mathematical Logic |
Том | 59 |
Номер выпуска | 7-8 |
DOI | |
Состояние | Опубликовано - 1 ноя 2020 |