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arXiv 2105.09604math.CTmath.LO
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关于等价关系范畴的一个注记

A note on the category of equivalence relations

Valentino Delle Rose, Luca San Mauro, Andrea Sorbi

摘要:

本文对自然数集合上的等价关系范畴$\mathbb{E}\mathrm{q}$作了初步的观察,其中两个等价关系$R,S$之间的态射是从$R$ -等价类集合到$S$ -等价类集合的映射,它是由一个可计算函数诱导的.我们还考虑了$\mathbb{E}\mathrm{q}$的一些满子范畴,如可计算可排等价关系范畴$\mathbb{E}\mathrm{q}(Σ^0_1)$(称为ceers),可共同计算可排等价关系范畴$\mathbb{E}\mathrm{q}(Π^0_1)$,以及对象为所谓的暗ceers加上具有多个等价类的ceers的范畴$\mathbb{E}\mathrm{q}(\mathrm{Dark}^*)$。虽然在所有这些范畴的单态与内射态射一致,我们表明,在$\mathbb{E}\mathrm{q}(Σ^0_1)$的满态与上态射一致,但在$\mathbb{E}\mathrm{q}(Π^0_1)$有满态,是不是上。此外,$\mathbb{E}\mathrm{q}$,$\mathbb{E}\mathrm{q}(Σ^0_1)$,和$\mathbb{E}\mathrm{q}(\mathrm{Dark}^*)$是封闭的有限产品,二进制余产品,和coequalizers,但我们给出了一个例子,两个态射在$\mathbb{E}\mathrm{q}(Π^0_1)$的coequalizer在$\mathbb{E}\mathrm{q}$不是一个对象的$\mathbb{E}\mathrm{q}(Π^0_1)$。

英文摘要:

We make some beginning observations about the category $\mathbb{E}\mathrm{q}$ of equivalence relations on the set of natural numbers, where a morphism between two equivalence relations $R,S$ is a mapping from the set of $R$-equivalence classes to that of $S$-equivalence classes, which is induced by a computable function. We also consider some full subcategories of $\mathbb{E}\mathrm{q}$, such as the category $\mathbb{E}\mathrm{q}(Σ^0_1)$ of computably enumerable equivalence relations (called ceers), the category $\mathbb{E}\mathrm{q}(Π^0_1)$ of co-computably enumerable equivalence relations, and the category $\mathbb{E}\mathrm{q}(\mathrm{Dark}^*)$ whose objects are the so-called dark ceers plus the ceers with finitely many equivalence classes. Although in all these categories the monomorphisms coincide with the injective morphisms, we show that in $\mathbb{E}\mathrm{q}(Σ^0_1)$ the epimorphisms coincide with the onto morphisms, but in $\mathbb{E}\mathrm{q}(Π^0_1)$ there are epimorphisms that are not onto. Moreover, $\mathbb{E}\mathrm{q}$, $\mathbb{E}\mathrm{q}(Σ^0_1)$, and $\mathbb{E}\mathrm{q}(\mathrm{Dark}^*)$ are closed under finite products, binary coproducts, and coequalizers, but we give an example of two morphisms in $\mathbb{E}\mathrm{q}(Π^0_1)$ whose coequalizer in $\mathbb{E}\mathrm{q}$ is not an object of $\mathbb{E}\mathrm{q}(Π^0_1)$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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