{
  "aliases": [
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  "body": "\n## Summary\n\nIn mathematics, a **cocountable** [[subset|0BJR9QR08E]] of a set $X$ is a subset $Y$ whose [[complement|0RKF1ZT5JJ]] in $X$ is a [[countable set|01TQB88H4C]]. In other words, $Y$ contains all but countably many elements of $X$. Since the rational numbers are a countable subset of the reals, for example, the irrational numbers are a cocountable subset of the reals. If the complement is finite, then one says $Y$ is cofinite.\n",
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  "name": "Cocountability",
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