Finite Cartesian power of a countable set
= Finite Cartesian power of a countable set
{title2=$B^m$}
A finite <Cartesian product> of <countable sets> is countable. For a fixed finite exponent $m$, index tuples in $\mathbb N^m$ can be listed by increasing maximum coordinate, with each group finite. If $B$ is countably infinite and $m>0$, its power $B^m$ is also countably infinite.