Zermelo's postulate ZermelosPostulate 2002-12-09 03:04:15 2006-09-13 21:37:08 Theorem % this is the default PlanetMath preamble. as your knowledge % of TeX increases, you will probably want to edit this, but % it should be fine as is for beginners. % almost certainly you want these \usepackage{amssymb} \usepackage{amsmath} \usepackage{amsfonts} % used for TeXing text within eps files %\usepackage{psfrag} % need this for including graphics (\includegraphics) %\usepackage{graphicx} % for neatly defining theorems and propositions %\usepackage{amsthm} % making logically defined graphics %\usepackage{xypic} % there are many more packages, add them here as you need them % define commands here If $\mathcal{F}$ is a disjoint family of nonempty sets, then there is a set $C$ which has exactly one element of each $A\in \mathcal{F}$ (i.e such that $A\cap C$ is a singleton for each $A\in \mathcal{F}$.) This is one of the many propositions that are equivalent to the axiom of choice.