Journal of Symbolic Logic
- J. Symbolic Logic
- Volume 69, Issue 2 (2004), 555-584.
Degrees of unsolvability of continuous functions
We show that the Turing degrees are not sufficient to measure the complexity of continuous functions on [0,1]. Computability of continuous real functions is a standard notion from computable analysis. However, no satisfactory theory of degrees of continuous functions exists. We introduce the continuous degrees and prove that they are a proper extension of the Turing degrees and a proper substructure of the enumeration degrees. Call continuous degrees which are not Turing degrees non-total. Several fundamental results are proved: a continuous function with non-total degree has no least degree representation, settling a question asked by Pour-El and Lempp; every non-computable f∈𝒞[0,1] computes a non-computable subset of ℕ; there is a non-total degree between Turing degrees a<T b iff b is a PA degree relative to a; 𝒮⊆ 2ℕ is a Scott set iff it is the collection of f-computable subsets of ℕ for some f∈𝒞[0,1] of non-total degree; and there are computably incomparable f,g∈𝒞[0,1] which compute exactly the same subsets of ℕ. Proofs draw from classical analysis and constructive analysis as well as from computability theory.
J. Symbolic Logic Volume 69, Issue 2 (2004), 555-584.
First available in Project Euclid: 19 April 2004
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Miller, Joseph S. Degrees of unsolvability of continuous functions. J. Symbolic Logic 69 (2004), no. 2, 555--584. doi:10.2178/jsl/1082418543. https://projecteuclid.org/euclid.jsl/1082418543.