We show that th Delta-0-2 enumeration degrees are dense. We also show that for everynonzero n-c. e. e-degree a, with n≥3, one can always find a nonzero 3-c. e. e-degree b such that b < a; on the other hand there is a nonzero omega-c. e. e-degree which bounds no nonzero n-c. e. e-degree.
Arslanov, M., Kalimullin, I.S., Sorbi, A. (2001). Density results in the Delta-0-2 e-degrees. ARCHIVE FOR MATHEMATICAL LOGIC, 40(8), 597-614 [10.1007/s001530100078].
Density results in the Delta-0-2 e-degrees
Sorbi, Andrea
2001-01-01
Abstract
We show that th Delta-0-2 enumeration degrees are dense. We also show that for everynonzero n-c. e. e-degree a, with n≥3, one can always find a nonzero 3-c. e. e-degree b such that b < a; on the other hand there is a nonzero omega-c. e. e-degree which bounds no nonzero n-c. e. e-degree.
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https://hdl.handle.net/11365/1082508