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COMPARING THE STRENGTH OF DIAGONALLY NONRECURSIVE FUNCTIONS IN THE ABSENCE OF
${\rm{\Sigma }}_2^0$ INDUCTION
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- Journal:
- The Journal of Symbolic Logic / Volume 80 / Issue 4 / December 2015
- Published online by Cambridge University Press:
- 22 December 2015, pp. 1211-1235
- Print publication:
- December 2015
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- Article
- Export citation
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We prove that the statement “there is a k such that for every f there is a k-bounded diagonally nonrecursive function relative to f” does not imply weak König’s lemma over
${\rm{RC}}{{\rm{A}}_0} + {\rm{B\Sigma }}_2^0$. This answers a question posed by Simpson. A recursion-theoretic consequence is that the classic fact that every k-bounded diagonally nonrecursive function computes a 2-bounded diagonally nonrecursive function may fail in the absence of 
${\rm{I\Sigma }}_2^0$.
