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\problems{Due: Wednesday, October 15th}{4}{6}

\begin{problem}
Draw the smallest graph (vertices plus edges) having one source and
one sink such that the graph is not series-parallel.  Prove it.
\end{problem}

\begin{problem}
Explain the notion of pseudotransitivity in the Nondeterminator. 
\end{problem}

\begin{problem}
Suppose the code for reading a shared location l in the
Nondeterminator is changed to the following:
\begin{tabbing}
    \hspace*{2em}\=\textbf{if}\ \=\textbf{if}\ \=\kill
    \texttt{read} a shared location $l$ by procedure $F$:\\
    \>\textbf{if} $\proc{Find-Set}(\id{writer}(l))$ is a P-bag \\
    \>\>\textbf{then} a determinacy race exists\\
    \>$\id{reader}(l)\leftarrow F$
\end{tabbing}
Are the errors made by this incorrect code false positives or false
negatives?  Give a simple example of what can go wrong.
\end{problem}

\end{document}
