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While thinking about my other question I found that it would be easier to talk about it if numbers just weren't so finite. There is a notion mentioned there in the comments of "list of congruences, possible or impossible" and I'm wondering if this idea has a more concise name.

So let's define a set $R$. Elements of $R$ are sequences $a_1, a_2, a_3, \ldots$ such that $\forall i. 0 \le a_i < i$ and for every finite $k$ the system
$$\left\{ \begin{array}{c} n\equiv a_1\pmod 1 \\ n\equiv a_2\pmod 2 \\ \vdots\\ n\equiv a_k\pmod k \\ \end{array} \right. $$ has a solution in n.

One can define the ring operations in a straightforward way, and there is an obvious injective ring homomorphism $\mathbb{Z}\to R$.

$R$ is uncountable, $R$ is compact as a subspace of Baire space $\mathbb{N^N}$.

My question is what $R$ and its elements are called.

Nikita
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1 Answers1

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Apparently, the elements are called profinite integers and the ring is called profinite completion of the integers.

Thanks to Gerry Myerson for the lead.

Nikita
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