countably infiniteCountablyInfinite2001-11-16 00:46:472002-06-14 16:22:21Definition\usepackage{amssymb}
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\usepackage{xypic}A set $S$ is countably infinite if there is a bijection between $S$ and $\mathbb{N}$.
As the name implies, any countably infinite set is both countable and infinite.
Countably infinite sets are also sometimes called \emph{denumerable}.