Abstract
We give a simple structural property which characterizes the r.e. sets whose (Turing) degrees are cappable. Since cappable degrees are incomplete, this may be viewed as a solution of Post's program, which asks for a simple structural property of nonrecursive r.e. sets which ensures incompleteness.
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Part of this research was done while the authors visited the Mathematical Sciences research Institute, Berkeley
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Ambos-Spies, K., Nies, A. Cappable recursively enumerable degrees and Post's program. Arch Math Logic 32, 51–56 (1992). https://doi.org/10.1007/BF01270394
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DOI: https://doi.org/10.1007/BF01270394