# Tagged Questions

**3**

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**2**answers

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### NNO = (first order) PA

Recall the definition of a Natural Numbers Object in a topos, and the first order axioms for Peano Arithmetic. I am more familiar with the first definition than the second, so I cannot tell from the ...

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**1**answer

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### Nelson natural number objects in a topos (say)

Nelson's predicative arithmetic (survey article) is a very weak system of arithmetic extending Robinson's $Q$ (Wikipedia).
We can have natural number objects in a topos, or even a merely finitely ...