diff --git a/chapter18.tex b/chapter18.tex
index 7106dec..25608f1 100644
--- a/chapter18.tex
+++ b/chapter18.tex
@@ -774,21 +774,21 @@ The following array corresponds to the above tree:
 \node at (14.5,0.5) {$1$};
 
 \footnotesize
-\node at (0.5,2.5) {$1$};
-\node at (1.5,2.5) {$2$};
-\node at (2.5,2.5) {$3$};
-\node at (3.5,2.5) {$4$};
-\node at (4.5,2.5) {$5$};
-\node at (5.5,2.5) {$6$};
-\node at (6.5,2.5) {$7$};
-\node at (7.5,2.5) {$8$};
-\node at (8.5,2.5) {$9$};
-\node at (9.5,2.5) {$10$};
-\node at (10.5,2.5) {$11$};
-\node at (11.5,2.5) {$12$};
-\node at (12.5,2.5) {$13$};
-\node at (13.5,2.5) {$14$};
-\node at (14.5,2.5) {$15$};
+\node at (0.5,2.5) {$0$};
+\node at (1.5,2.5) {$1$};
+\node at (2.5,2.5) {$2$};
+\node at (3.5,2.5) {$3$};
+\node at (4.5,2.5) {$4$};
+\node at (5.5,2.5) {$5$};
+\node at (6.5,2.5) {$6$};
+\node at (7.5,2.5) {$7$};
+\node at (8.5,2.5) {$8$};
+\node at (9.5,2.5) {$9$};
+\node at (10.5,2.5) {$10$};
+\node at (11.5,2.5) {$11$};
+\node at (12.5,2.5) {$12$};
+\node at (13.5,2.5) {$13$};
+\node at (14.5,2.5) {$14$};
 \end{tikzpicture}
 \end{center}
 
@@ -846,27 +846,27 @@ can be found as follows:
 \node at (14.5,0.5) {$1$};
 
 \footnotesize
-\node at (0.5,2.5) {$1$};
-\node at (1.5,2.5) {$2$};
-\node at (2.5,2.5) {$3$};
-\node at (3.5,2.5) {$4$};
-\node at (4.5,2.5) {$5$};
-\node at (5.5,2.5) {$6$};
-\node at (6.5,2.5) {$7$};
-\node at (7.5,2.5) {$8$};
-\node at (8.5,2.5) {$9$};
-\node at (9.5,2.5) {$10$};
-\node at (10.5,2.5) {$11$};
-\node at (11.5,2.5) {$12$};
-\node at (12.5,2.5) {$13$};
-\node at (13.5,2.5) {$14$};
-\node at (14.5,2.5) {$15$};
+\node at (0.5,2.5) {$0$};
+\node at (1.5,2.5) {$1$};
+\node at (2.5,2.5) {$2$};
+\node at (3.5,2.5) {$3$};
+\node at (4.5,2.5) {$4$};
+\node at (5.5,2.5) {$5$};
+\node at (6.5,2.5) {$6$};
+\node at (7.5,2.5) {$7$};
+\node at (8.5,2.5) {$8$};
+\node at (9.5,2.5) {$9$};
+\node at (10.5,2.5) {$10$};
+\node at (11.5,2.5) {$11$};
+\node at (12.5,2.5) {$12$};
+\node at (13.5,2.5) {$13$};
+\node at (14.5,2.5) {$14$};
 \end{tikzpicture}
 \end{center}
 
-Node 5 is at position 3, node 8 is at position 6,
+Node 5 is at position 2, node 8 is at position 5,
 and the node with lowest level between
-positions $3 \ldots 6$ is node 2 at position 4
+positions $2 \ldots 5$ is node 2 at position 3
 whose level is 2.
 Thus, the lowest common ancestor of
 nodes 5 and 8 is node 2.