@MISC{Ferreira_asimple, author = {Fernando Ferreira}, title = {A simple proof of Parsons' theorem}, year = {} }

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Abstract

Let I# 1 be the fragment of elementary Peano Arithmetic in which induction is restricted to #1-formulas. More than three decades ago, Charles Parsons showed that the provably total functions of I# 1 are exactly the primitive recursive functions. In this paper, we observe that Parsons' result is a consequence of Herbrand's theorem concerning the of universal theories. We give a self-contained proof requiring only basic knowledge of mathematical logic.