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Questions related to computability theory, a.k.a. recursion theory

2 votes
2 answers
360 views

how does Kleene-Post show two languages that are not Turing reducible to each other?

I'm having difficulty understanding the proof of the Kleene-Post result. It purports to construct two languages that are not Turing reducible to each other, using a diagonalization argument. I've seen …
3 votes

how does Kleene-Post show two languages that are not Turing reducible to each other?

(For the below, I referred extensively to this github repo as well as private communication with @aozgaa) Languages can be represented as infinite-length bitstrings (ILB). We will use the two intercha …
xdavidliu's user avatar
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0 votes

EQtm is not mapping reducible to its complement

Suppose $EQ_\mathrm{TM} \leq_\mathrm{m} \overline{EQ_\mathrm{TM}}$. Then there exists an $f : \Sigma^\star \rightarrow \Sigma^\star$ such that $f(w) \in EQ_\mathrm{TM}$ if and only if $w \in \overline …
xdavidliu's user avatar
  • 858
6 votes

Show that the single-tape TMs that can not write on the portion of the tape containing the i...

Actually, you don't need to construct the DFA, you just need to show that it exists using the Myhill Nerode theorem. Here's how: given a machine $M$ that cannot write on its input, suppose the input h …
xdavidliu's user avatar
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0 votes

Show a TM-recognizable language of TMs can be expressed by TM-description language of equiva...

Here's a much simpler answer that uses the same idea as @xskxzr's answer. I found the bijection used in that answer not really necessary: it's much simpler to just directly store the number of steps i …
xdavidliu's user avatar
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