We prove that each ∑02 set which is hypersimple relative to 0′ is noncuppable in the structure of the ∑02numeration degrees. This gives a connection between properties of ∑02ets under inclusion and and the ∑02 enumeration degrees. We also prove that some low non-computably enumerable enumeration degree contains no set which is simple relative to 0′.
Nies, A., Sorbi, A. (2000). Structural properties and Sigma^0_2 enumeration degrees. THE JOURNAL OF SYMBOLIC LOGIC, 65(1), 285-292 [10.2307/2586537].
Structural properties and Sigma^0_2 enumeration degrees
Sorbi, Andrea
2000-01-01
Abstract
We prove that each ∑02 set which is hypersimple relative to 0′ is noncuppable in the structure of the ∑02numeration degrees. This gives a connection between properties of ∑02ets under inclusion and and the ∑02 enumeration degrees. We also prove that some low non-computably enumerable enumeration degree contains no set which is simple relative to 0′.File in questo prodotto:
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https://hdl.handle.net/11365/1082589