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Reports on Mathematical Logic

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No. 39

Matthias Schirn, Karl-Georg Niebergall

**Finitism = PRA? On a Thesis of
W.W. Tait**

A b s t r a c t. In his paper `Finitism' (1981), W.W.~Tait maintained that the chief difficulty for everyone who wishes to understand Hilbert's
conception of finitist mathematics is this: to specify the sense of the provability of general statements about the natural
numbers without presupposing infinite totalities. Tait further argued that all finitist reasoning is essentially primitive
recursive. In our paper, we attempt to show that his thesis ``The finitist functions are precisely the primitive recursive functions'' is
disputable and that another, likewise defended by him, is untenable. The second thesis is that the finitist theorems are precisely those
$\Pi^0_1$-sentences that can be proved in (QF-IA).

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