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arXiv 2003.02250math.LO
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关于序群的半有界扩张

On semibounded expansions of ordered groups

Pantelis E. Eleftheriou, Alex Savatovsky

摘要:

我们探讨“半有界”的任意序群的扩展,即扩展,不定义一个领域的整个宇宙。证明了如果$\mathcal R=\langle R, <, +, \dots\rangle$是半有界的o-极小结构,且$P\subseteq R$是满足一定驯服条件的集合,则$\langle \cal R, P\rangle$保持半有界.示例包括当$\mathcal{R}=\langle \mathbb R,<,+, (x\mapsto λx)_{λ\in \mathbb R}, \cdot_{ [0, 1]^2} \rangle$和$P= 2^\mathbb Z$或$P$是迭代序列时的情况。作为应用,我们得到了在这种$\langle \mathcal R, P\rangle$中可定义的光滑函数在$\mathcal R$中也可定义.

英文摘要:

We explore "semibounded" expansions of arbitrary ordered groups; namely, expansions that do not define a field on the whole universe. We show that if $\mathcal R=\langle R, <, +, \dots\rangle$ is a semibounded o-minimal structure and $P\subseteq R$ a set satisfying certain tameness conditions, then $\langle \cal R, P\rangle$ remains semibounded. Examples include the cases when $\mathcal{R}=\langle \mathbb R,<,+, (x\mapsto λx)_{λ\in \mathbb R}, \cdot_{ [0, 1]^2} \rangle$, and $P= 2^\mathbb Z$ or $P$ is an iteration sequence. As an application, we obtain that smooth functions definable in such $\langle \mathcal R, P\rangle$ are definable in $\mathcal R$.

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