\documentclass[a4paper]{scrartcl}
\usepackage{fuzz}

\begin{document}

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

\begin{schema}{State}
  state : TEST \rel TEST
\end{schema}

\begin{schema}{Init}
  State'\\
  \where
  state' = \{\}
\end{schema}

\begin{schema}{Inc}
  \Delta State\\
  pos? : TEST\\
  value? : TEST\\
  \where
  \# state \leq 1\\
  state' = state \oplus \{pos? \mapsto value?\}
\end{schema}

\begin{schema}{Invert}
  \Delta State\\
  \where
  state' = state \inv\\
\end{schema}

\end{document}
