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Local Density of Kleene Degrees
Authors:Hisato Muraki
Abstract:Concerning Post's problem for Kleene degrees and its relativization, Hrbacek showed in [1] and [2] that if V = L, then Kleene degrees of coanalytic sets are dense, and then for all K ?ωω, there are N1 sets which are Kleene semirecursive in K and not Kleene recursive in each other and K. But the density of Kleene semirecursive in K Kleene degrees is not obtained from these theorems. In this note, we extend these theorems by showing that if V = L, then for all K ? ωω, Kleene semirecursive in K Kleene degrees are dense above K.
Keywords:Kleene reducibility  Relativized Post's problem  Constructible universe
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