scan/free pointer mixup, issue #173

Author: jsiek

book.tex

@@ -12748,8 +12748,8 @@ \subsection{Graph Copying via Cheney's Algorithm}
 Figure~\ref{fig:cheney} shows several snapshots of the ToSpace as the
 copy progresses. The queue is represented by a chunk of contiguous
 memory at the beginning of the ToSpace, using two pointers to track
-the front and the back of the queue, called the \emph{free pointer}
-and the \emph{scan pointer}, respectively. The algorithm starts by
+the front and the back of the queue, called the \emph{scan pointer}
+and the \emph{free pointer}, respectively. The algorithm starts by
 copying all tuples that are immediately reachable from the root set
 into the ToSpace to form the initial queue.  When we copy a tuple, we
 mark the old tuple to indicate that it has been visited. We discuss