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- MARIA L. AFFATATO, ANDREA SORBI, Lachlan Nondiamond
- 2007

We give an alternative and more informative proof that every nontrivial Σ 0 2-enumeration degrees is the meet of two incomparable Σ 0 2-degrees, which allows us to show the stronger result that for every incomplete Σ 0 2-enumeration degree a, there exist enumeration degrees x 1 and x 2 such that a, x 1 , x 2 are incomparable, and for all b ≤ a, b = (b ∪ x… (More)

We show that the first order theory of the Σ 0 2 s-degrees is undecidable. Via isomorphism of the s-degrees with the Q-degrees, this also shows that the first order theory of the Π 0 2 Q-degrees is undecidable. Together with a result of Nies, the proof of the undecidability of the Σ 0 2 s-degrees yields a new proof of the known fact (due to Downey, LaForte… (More)

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