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Computability and Logic

Computability and Logic

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24<br />

Decidability of Arithmetic without Multiplication<br />

Arithmetic is not decidable: the set V of code numbers of sentences of the language<br />

L of arithmetic that are true in the st<strong>and</strong>ard interpretation is not recursive (nor even<br />

arithmetical). But for some sublanguages L* of L, if we consider the elements of V that<br />

are code numbers of sentences of L*, then the set V* of such elements is recursive:<br />

arithmetic without some of the symbols of its language is decidable. A striking case<br />

is Presburger arithmetic, or arithmetic without multiplication. The present chapter is<br />

entirely devoted to proving its decidability.<br />

We have used (true) arithmetic to mean the set of sentences of the language<br />

of arithmetic L ={0,

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