diff -r 6d9c960a2b26 -r bfc8703b1527 hws/hw09.tex
--- a/hws/hw09.tex	Sat Dec 07 00:57:23 2019 +0000
+++ b/hws/hw09.tex	Sat Dec 14 17:57:43 2019 +0000
@@ -60,7 +60,8 @@
 }
 \end{lstlisting}
 
-  
+\item What is the difference between a parse tree and an abstract
+  syntax tree? Give some simple examples for each of them.