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Structural properties and Σ20 enumeration degrees
Published online by Cambridge University Press: 12 March 2014
Abstract
We prove that each Σ20 set which is hypersimple relative to ∅′ is noncuppable in the structure of the Σ20 enumeration degrees. This gives a connection between properties of Σ20 sets under inclusion and and the Σ20 enumeration degrees. We also prove that some low non-computably enumerable enumeration degree contains no set which is simple relative to ∅′.
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- Copyright © Association for Symbolic Logic 2000
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