DEF-FIN. Finite and Infinite Set.
$X$ is finite if there is a bijection from $X$ to a natural number, i.e.
\[\lvert X\rvert = n\]for some $n\in\N$.
$X$ is infinite if it is not finite.
DEF-FIN. Finite and Infinite Set.
$X$ is finite if there is a bijection from $X$ to a natural number, i.e.
\[\lvert X\rvert = n\]for some $n\in\N$.
$X$ is infinite if it is not finite.