countable Countable 2001-11-16 00:40:40 2002-02-27 23:38:07 Definition \usepackage{amssymb} \usepackage{amsmath} \usepackage{amsfonts} \usepackage{graphicx} \usepackage{xypic} A set $S$ is countable if there exists a bijection between $S$ and some subset of $\mathbb{N}$. All finite sets are countable.