代数结构的双可嵌入范畴
On bi-embeddable categoricity of algebraic structures
摘要：
在几类可数结构中，已知每个超算术结构都具有可计算表示，直到双嵌入性。在这篇文章中，我们研究了两个这样的类，线性序和布尔代数类的双嵌入结构之间的嵌入的复杂性。证明了如果$\mathcal L$是Hausdorff秩$n$的可计算线性序，则对于它的每一个双嵌入拷贝，都存在一个可计算的嵌入，其嵌入在原子图的$2n-1$跳跃中.我们还证明了这是最好的方法：设$\mathcal L$是Hausdorff秩$n\geq 1$的可计算线性序，则$\mathbf 0^{(2n-2)}$不计算它和它的所有可计算双嵌入副本之间的嵌入。证明了对于非超原子的布尔代数，其所有可计算双嵌入副本之间不存在超算术度计算嵌入。另一方面，如果一个可计算布尔代数是超原子的，则存在一个最小可计算序数$α$，使得$\mathbf 0^{(α)}$计算其所有可计算双嵌入副本之间的嵌入。在这个证明中使用的主要技术是一个新的变化阿什和骑士的对结构定理。
英文摘要：
In several classes of countable structures it is known that every hyperarithmetic structure has a computable presentation up to bi-embeddability. In this article we investigate the complexity of embeddings between bi-embeddable structures in two such classes, the classes of linear orders and Boolean algebras. We show that if $\mathcal L$ is a computable linear order of Hausdorff rank $n$, then for every bi-embeddable copy of it there is an embedding computable in $2n-1$ jumps from the atomic diagrams. We furthermore show that this is the best one can do: Let $\mathcal L$ be a computable linear order of Hausdorff rank $n\geq 1$, then $\mathbf 0^{(2n-2)}$ does not compute embeddings between it and all its computable bi-embeddable copies. We obtain that for Boolean algebras which are not superatomic, there is no hyperarithmetic degree computing embeddings between all its computable bi-embeddable copies. On the other hand, if a computable Boolean algebra is superatomic, then there is a least computable ordinal $α$ such that $\mathbf 0^{(α)}$ computes embeddings between all its computable bi-embeddable copies. The main technique used in this proof is a new variation of Ash and Knight's pairs of structures theorem.
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