Every ∆2-Set is Natural, up to Turing Equivalence
نویسنده
چکیده
The Turing degrees of ∆2 sets as well as the degrees of sets in certain upper segments of the Ershov hierarchy are characterized. In particular, it is shown that, up to Turing equivalence and admissible indexing, the noncomputable ∆2 sets are exactly the decision problems of countable partial orders of tree shape with branches of positive finite length only.
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تاریخ انتشار 2010