is there any hierarchy for many-one complete languages of re (re-complete languages)? how can we propose a categorization for these languages? depending on what measures?
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Under many-one reductions by arbitrary total computable functions, HALT is the prototypical re-complete problem. A common technique for showing that some problem is undecidable (though not usually expressed in these terms) is to show that it is re-hard by reduction from HALT. Using a weaker class of allowed reductions may lead to fewer problems being complete, but HALT is still re-complete even under linear-time many-one reductions. For some reason, this terminology is much less used (to the point of not being used at all) in computability than in complexity. |
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