算术模型的结构复杂性
The structural complexity of models of arithmetic
摘要:
我们计算了Peano算术可数模型的可能Scott秩。我们发现,没有非标准的模型可以有斯科特秩小于$ω$和真正的算术的非标准模型必须有斯科特秩大于$ω$。除此之外,没有任何限制。通过给出从线性序类到$\mathrm{PA}$的任意完备$T$的模型的规范结构$ω$ -跳的$Δ^{\mathrm{in}}_{1}$双可解释性的约化,我们证明了每个可数序数$α>ω$都可实现为$T$的模型的Scott秩.
英文摘要:
We calculate the possible Scott ranks of countable models of Peano arithmetic. We show that no non-standard model can have Scott rank less than $ω$ and that non-standard models of true arithmetic must have Scott rank greater than $ω$. Other than that there are no restrictions. By giving a reduction via $Δ^{\mathrm{in}}_{1}$ bi-interpretability from the class of linear orderings to the canonical structural $ω$-jump of models of an arbitrary completion $T$ of $\mathrm{PA}$ we show that every countable ordinal $α>ω$ is realized as the Scott rank of a model of $T$.
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