1 results
A characterization of the δ20 hyperhyperimmune sets
-
- Journal:
- The Journal of Symbolic Logic / Volume 73 / Issue 4 / December 2008
- Published online by Cambridge University Press:
- 12 March 2014, pp. 1407-1415
- Print publication:
- December 2008
-
- Article
- Export citation
-
Let A be an infinite
set and let K be creative: we show that K ≤QA if and only if K
A. (Here ≤Q denotes Q-reducibility, and is the subreducibility of ≤Q obtained by requesting that Q-reducibility be provided by a computable function f such that Wf(x) ∩ Wf(y) = ∅. if x ≠ y.) Using this result we prove that A is hyperhyperimmune if and only if no subset B of A is s-complete, i.e., there is no subset B of A such that 
≤sB, where ≤s denotes s-reducibility, and denotes the complement of K.
set and let 
≤