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A numbering is first defined as a function from ${\displaystyle \mathbb {N} }$ to S, but the example that follows is a function from S to ${\displaystyle \mathbb {N} }$. AmirOnWiki ( talk) 08:05, 16 April 2017 (UTC) reply

That numbering is a bijection, unlike most, so it could be specified in either direction. The article had written it in the other order, which wasn't literally correct but is more clean. I reversed it, so now it is literally right, but at the cost of more convoluted prose. — Carl ( CBM ·  talk) 15:48, 16 April 2017 (UTC) reply