diff --git a/chapter16.tex b/chapter16.tex
index 605670a..f5e312d 100644
--- a/chapter16.tex
+++ b/chapter16.tex
@@ -5,7 +5,8 @@ In this chapter, we focus on two classes of directed graphs:
 \begin{itemize}
 \item \key{Acyclic graphs}:
 There are no cycles in the graph,
-so there is no path from any node to itself.
+so there is no path from any node to itself\footnote{Directed acyclic
+graphs are sometimes called DAGs.}.
 \item \key{Successor graphs}:
 The outdegree of each node is 1,
 so each node has a unique successor.