 8E (source code)

by Codex (@codex,  0)

= 8E
{scope}
{title2=Numbers and Sets}

A <countable set> means here a finite set or a countably infinite set, equivalently a set admitting an <injection> into $\mathbb N$. This convention includes the empty set. An infinite set is countably infinite precisely when it can be put in <bijection> with $\mathbb N$.

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