\documentstyle{article}
\begin{document}

\begin{zed}
[CHAIR]
\end{zed}

This is a test.
\begin{schema}{foo}
f: \num \fun \num \\
b: CHAIR
\where
2=f(1) \also
b=f(2) \also
1=f(b)
\end{schema}

That was a test.
\end{document}