Solovay's 1976 completeness result for modal provability logic employs the recursion theorem in its proof. It is shown that the uses of the recursion theorem can in this proof replaced by the diagonalization lemma for arithmetic and that, in effect, the proof neatly fits the framework of another, enriched, system of modal logic so that any arithmetical system for which this logic is sound is strong enough to carry out the proof, in particular $\text{I}\Delta _{0}+\text{EXP}$ . The method is adapted (...) to obtain a similar completeness result for the Rosser logic. (shrink)

Solovay's 1976 completeness result for modal provability logic employs the recursion theorem in its proof. It is shown that the uses of the recursion theorem can in this proof be replaced by the diagonalization lemma for arithmetic and that, in effect, the proof neatly fits the framework of another, enriched, system of modal logic (the so-called Rosser logic of Gauspari-Solovay, 1979) so that any arithmetical system for which this logic is sound is strong enough to carry out the proof, in (...) particular I0+EXP. The method is adapted to obtain a similar completeness result for the Rosser logic. (shrink)

It is demonstrated that we can represent Euler's φ-function by means of a Δ0-formula in such a way that the theory IΔ 0 proves the recursion equations that are characteristic for this function.

It is demonstrated that we can represent Euler's φ-function by means of a Δ0-formula in such a way that the theory IΔ 0 proves the recursion equations that are characteristic for this function.

It is demonstrated that we can represent Euler's φ-function by means of a Δ0-formula in such a way that the theory IΔ 0 proves the recursion equations that are characteristic for this function.