Notre Dame Journal of Formal Logic
- Notre Dame J. Formal Logic
- Volume 52, Number 1 (2011), 21-38.
Characterizing the Join-Irreducible Medvedev Degrees
We characterize the join-irreducible Medvedev degrees as the degrees of complements of Turing ideals, thereby solving a problem posed by Sorbi. We use this characterization to prove that there are Medvedev degrees above the second-least degree that do not bound any join-irreducible degrees above this second-least degree. This solves a problem posed by Sorbi and Terwijn. Finally, we prove that the filter generated by the degrees of closed sets is not prime. This solves a problem posed by Bianchini and Sorbi.
Notre Dame J. Formal Logic, Volume 52, Number 1 (2011), 21-38.
First available in Project Euclid: 13 December 2010
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Shafer, Paul. Characterizing the Join-Irreducible Medvedev Degrees. Notre Dame J. Formal Logic 52 (2011), no. 1, 21--38. doi:10.1215/00294527-2010-034. https://projecteuclid.org/euclid.ndjfl/1292249608