added a question about graph on page 32

book.tex

@@ -1707,6 +1707,8 @@ interferes with $x$, $y$ interferes with $z$, and $w$ interferes with
 $y$ and $z$.  The resulting interference graph is shown in
 Figure~\ref{fig:interfere}.
 
+\marginpar{I don't think this graph is correct. If Z interferes with X,
+shouldn't there be an edge that connects them?}
 \begin{figure}[tbp]
 \large
 \[