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arxiv: 1401.3823 · v2 · pith:VU7DK2NEnew · submitted 2014-01-16 · 🧮 math.LO

Comparing the strength of diagonally non-recursive functions in the absence of Sigma⁰₂ induction

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keywords diagonallynon-recursiveboundedfunctionmathrmsigmaabsenceevery
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We prove that the statement "there is a $k$ such that for every $f$ there is a $k$-bounded diagonally non-recursive function relative to $f$" does not imply weak K\"onig's lemma over $\mathrm{RCA}_0 + \mathrm{B}\Sigma^0_2$. This answers a question posed by Simpson. A recursion-theoretic consequence is that the classic fact that every $k$-bounded diagonally non-recursive function computes a $2$-bounded diagonally non-recursive function may fail in the absence of $\mathrm{I}\Sigma^0_2$.

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