Abstract
We show that the subsystem of Peano Arithmetic containing only induction for Σ2 formulas suffices to prove the existence of a recursively enumerable set of high, incomplete degree. By a result of Mytilinaios and Slaman, bounding for Σ2 formulas does not suffice to prove that such a set exists. In contrast, by a result of Groszek and Slaman, induction for Σ1 formulas suffices to carry out any Friedberg-style finite injury priority argument.
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© 1990 Springer-Verlag
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Groszek, M., Mytilinaios, M. (1990). Σ2-induction and the construction of a high degree. In: Ambos-Spies, K., Müller, G.H., Sacks, G.E. (eds) Recursion Theory Week. Lecture Notes in Mathematics, vol 1432. Springer, Berlin, Heidelberg. https://doi.org/10.1007/BFb0086119
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DOI: https://doi.org/10.1007/BFb0086119
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