diff -r 7ed2a25dd115 -r ca349cfe3474 hws/hw01.tex
--- a/hws/hw01.tex	Tue Oct 28 12:24:11 2014 +0000
+++ b/hws/hw01.tex	Sat Nov 01 15:06:41 2014 +0000
@@ -34,14 +34,16 @@
 
 \item Assume the concatenation operation of two strings is written as
   $s_1 @ s_2$. Define the operation of \emph{concatenating}, written
-  $\_ \,@\, \_$ two sets of strings.
+  $\_ \,@\, \_$, two sets of strings.
 
-\item Assume a set $A$ contains 4 strings and a set $B$ 7 strings, how
-  many strings are in $A \,@\, B$?
+\item Assume a set $A$ contains 4 strings and a set $B$ 7 strings. None
+  of the strings is the empty string. How many strings are in $A \,@\, B$?
 
 \item How is the power of a language defined? (Hint: There are two
   rules, one for $\_^0$ and one for $\_^{n+1}$.)
 
+\item Let $A = \{[], [a], [b], [c]\}$. How many strings are in $A^4$?
+
 \item How many regular expressions are there to match the string
   $abc$? How many if they cannot include $\epsilon$ and $\varnothing$?
   How many if they are also not allowed to contain stars? How many if