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Title: Arithmetic complexity via effective names for random sequences
Authors: Kjos-Hanssen, B.
Stephan, F. 
Teutsch, J.
Keywords: Arithmetical hierarchy
Computable randomness
Schnorr randomness
Issue Date: Aug-2012
Citation: Kjos-Hanssen, B., Stephan, F., Teutsch, J. (2012-08). Arithmetic complexity via effective names for random sequences. ACM Transactions on Computational Logic 13 (3) : -. ScholarBank@NUS Repository.
Abstract: We investigate enumerability properties for classes of sets which permit recursive, lexicographically increasing approximations, or left-r.e. sets. In addition to pinpointing the complexity of left-r.e. Martin-Löf, computably, Schnorr, and Kurtz random sets, weakly 1-generics and their complementary classes, we find that there exist characterizations of the third and fourth levels of the arithmetic hierarchy purely in terms of these notions. More generally, there exists an equivalence between arithmetic complexity and existence of numberings for classes of left-r.e. sets with shift-persistent elements. While some classes (such as Martin- Löf randoms and Kurtz nonrandoms) have left-r.e. numberings, there is no canonical, or acceptable, left-r.e. numbering for any class of left-r.e. randoms. Finally, we note some fundamental differences between left-r.e. numberings for sets and reals. © 2012 ACM 1529-3785/2012/08-ART24.
Source Title: ACM Transactions on Computational Logic
ISSN: 15293785
DOI: 10.1145/2287718.2287724
Appears in Collections:Staff Publications

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