Hyperimmune-free Degrees beyond Ω
نویسندگان
چکیده
An α-degree is hyperimmune-free if it does not contain a hyperimmune set. We study the existence problem of a hyperimmunefree α-degree for an admissible ordinal α, and show that the underlying structure of an admissible ordinal determines the existence and cardinality of the collection of hyperimmune-free α-degrees. The combinatorial principle 3 is demonstrated to play a key role in answering this ques-
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تاریخ انتشار 2008