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+\section{Components}
+Our chip consists of the following static components:
+
+\begin{itemize}
+	\item An ALU: $\ALUOp \times \Word8 \times \Word8 \to \Word8$.
+	\item The program memory $\prog$: $\Prog \eqdef \Word6^{256}$.
+\end{itemize}
+
+And these volatile components:
+
+\begin{itemize}
+	\item A memory $\mem$: $\Mem \eqdef \Word8^{256}$. Individual words or cells
+		are addressed with one word. We write $\mem.n$ for the cell in $\mem$ at
+		address $n$. We write $\update{\mem}{n\mapsto k}$ for the memory $\mem'$
+		with
+		$$
+			\mem'.i = \begin{cases}
+				k      & \text{if $i=n$,}\\
+				\mem.i & \text{otherwise.}
+			\end{cases}
+		$$
+	\item The accumulators $\acc1$ and $\acc2$ are located at address $0$ and
+		$1$ of the memory, respectively.
+	\item The program counter $\pc$ is located at address $2$ of the memory.
+\end{itemize}
+
+A state $\st$ can be seen as a tuple $(\prog,\mem)$. We define the set of all
+states $\State \eqdef \Word6^{256} \times \Word8^{256}$. An instruction is a
+function $\Mem\to\Mem$. The instruction cycle is a function $\State\to\State$.