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Proceedings of the American Mathematical Society
Article . 1994 . Peer-reviewed
Data sources: Crossref
Proceedings of the American Mathematical Society
Article . 1994 . Peer-reviewed
Data sources: Crossref
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Permutations and presentations

Authors: Rodney G. Downey; Peter Cholak;

Permutations and presentations

Abstract

We say that an automorphismΦ\PhiofE∗{\mathcal {E}^ \ast }(the lattice of recursively enumerable sets modulo the finite sets) isinducedby a permutationpiff for alle,Φ(We)=∗p(We)\Phi ({W_e}){ = ^ \ast }p({W_e}). A permutationhis called apresentationofΦ\Phiiff for alle,Φ(We)=∗Wh(e)\Phi ({W_e}){ = ^\ast }{W_{h(e)}}. In this paper, we will explore the degree-theoretic connections between these two notions. Using a new proof of the well-known fact that every automorphism is induced by a permutationp, we show that such apcan be found recursively inh⊕∅h \oplus \emptyset, wherehis a presentation ofΦ\Phi. The main result of the paper is to show that there is an effective automorphism ofE∗{\mathcal {E}^ \ast }which is not induced by aΔ2{\Delta _2}-permutation.

Keywords

Recursively (computably) enumerable sets and degrees, lattice of r.e. sets modulo the finite sets, Other degrees and reducibilities in computability and recursion theory, automorphism group, degrees of unsolvability, permutation, presentation

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
Average
Average
Average
bronze