>>557
>両側無限列あるいは双方向無限列 (doubly or bi-infinite sequence) である（前記>>556）

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下記
「For example, the sequence (a_{n})_{n=1}^{∞ } is the same as the sequence (a_{n})_{n∈ N }, and does not contain an additional term "at infinity".」
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https://en.wikipedia.org/wiki/Sequence
Sequence

The limits ∞ and -∞ are allowed, but they do not represent valid values for the index, only the supremum or infimum of such values, respectively.
For example, the sequence (a_{n})_{n=1}^{∞ } is the same as the sequence (a_{n})_{n∈ N }, and does not contain an additional term "at infinity".
The sequence (a_{n})_{n=-∞ }^{∞ } is a bi-infinite sequence, and can also be written as (・・・ ,a_{-1},a_{0},a_{1},a_{2},・・・ ).