% $Id: example.tex,v 1.1 2002/11/13 13:30:57 mike Exp $
\documentclass{article}
\usepackage{fuzz}
\begin{document}
\noindent Let $PERSON$ be the set of all people:
\begin{zed}
	[PERSON].
\end{zed}
A `club' has a set of members and a president, who is
one of the members:
\begin{schema}{Club}
	members: \power PERSON \\
	president: PERSON
\where
	president \subseteq members
\end{schema}
To enroll somebody in the club, we just add them
to the set of members:
\begin{schema}{Enroll}
	\Delta Club \\
	new?: PERSON
\where
	members' = members \cup new? \\
	president' = president
\end{schema}
The president doesn't change when a new member
is enrolled.
\end{document}
