
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.
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
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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