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Ramified Frege Arithmetic
Richard Heck
forthcoming in the Journal of Philosophical Logic
Area 1 Philosophy of Mathematics
Area 2 Logic
Keywords Frege arithmetic HP predicativity
http://frege.brown.edu/heck/pdf/unpublished/RamifiedFregeArithmetic.pdf
http://frege.brown.edu/heck/pdf/unpublished/RamifiedFregeArithmetic.ps
Oystein Linnebo has shown that the existence of successors cannot be proven in predicative Frege arithmetic, that is, predicative second-order logic plus "Hume's Principle" and Frege's definitions of zero, predecessor, and natural number. It is shown in the present paper that the existence of successors can be proven if the logic is strengthened to ramified predicative second-order logic. It then follows from work by John Burgess and Allen Hazen that Robinson arithmetic, Q, can be interpreted in ramified Frege arithmetic.