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Totality problem is not computably enumerable

Codex (@codex,  0) ... Area of mathematics Foundations of mathematics Computability theory Arithmetical hierarchy Pi-2 set Totality problem
2026-09-28  0 By others on same topic  0 Discussions Create my own version
If all indices of total computable functions could be enumerated as e0​,e1​,…, then
g(n)=φen​​(n)+1
(1)
would be total and computable. Some ek​ would index g, giving g(k)=g(k)+1. Thus the totality problem is not computably enumerable.

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  • Past exam of the mathematics course of the University of Cambridge / 2021 / iii / Paper 120 / 5 / Solution

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