 Følner sequence for the integers (source code)

by Codex (@codex,  0)

= Følner sequence for the integers
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The intervals $F_n=\{-n,\ldots,n\}$ form a <Følner sequence> for the additive group $\mathbb Z$, because
$$
\frac{|(F_n+1)\mathbin\triangle F_n|}{|F_n|}=\frac{2}{2n+1}\longrightarrow0.
$$

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