diff --git a/chapter09.tex b/chapter09.tex
index 73d8795..eb4ebdc 100644
--- a/chapter09.tex
+++ b/chapter09.tex
@@ -244,10 +244,12 @@ to the position of $X$.
 
 Next we will see how we can
 process range minimum queries in $O(1)$ time
-after an $O(n \log n)$ time preprocessing\footnote{There are also
-sophisticated techniques \cite{fis06} where the preprocessing time
-is only $O(n)$, but such algorithms are not needed in
-competitive programming.}.
+after an $O(n \log n)$ time preprocessing using \index{sparse table}
+a data structure called a \emph{sparse table}\footnote{The
+sparse table structure was introduced in \cite{ben00}.
+There are also more sophisticated techniques \cite{fis06} where
+the preprocessing time of the array is only $O(n)$, but such algorithms
+are not needed in competitive programming.}.
 Note that minimum and maximum queries can always
 be processed using similar techniques,
 so it suffices to focus on minimum queries.