diff --git a/chapter19.tex b/chapter19.tex
index e3276b5..1163cec 100644
--- a/chapter19.tex
+++ b/chapter19.tex
@@ -632,13 +632,13 @@ The search can be made more efficient by using
 \key{heuristics} that attempt to guide the knight so that
 a complete tour will be found quickly.
 
-\subsubsection{Warnsdorff's rule}
+\subsubsection{Warnsdorf's rule}
 
 \index{heuristic}
-\index{Warnsdorff's rule}
+\index{Warnsdorf's rule}
 
-\key{Warnsdorff's rule}\footnote{This heuristic was proposed
-in Warnsdorff's book \cite{war23} in 1823.} is a simple and effective heuristic
+\key{Warnsdorf's rule}\footnote{This heuristic was proposed
+in Warnsdorf's book \cite{war23} in 1823.} is a simple and effective heuristic
 for finding a knight's tour.
 Using the rule, it is possible to efficiently construct a tour
 even on a large board.
@@ -660,7 +660,7 @@ possible squares to which the knight can move:
 \node at (3.5,1.5) {$d$};
 \end{tikzpicture}
 \end{center}
-In this situation, Warnsdorff's rule moves the knight to square $a$,
+In this situation, Warnsdorf's rule moves the knight to square $a$,
 because after this choice, there is only a single possible move.
 The other choices would move the knight to squares where
 there would be three moves available.