--- a/handouts/ho02.tex	Sat Oct 01 23:34:37 2016 +0100
+++ b/handouts/ho02.tex	Sun Oct 02 14:07:42 2016 +0100
@@ -64,7 +64,7 @@
     axis lines=left,
     width=6.5cm,
     height=5cm]
-\addplot[green,mark=square*,mark options={fill=white}] table {re2.data};
+\addplot[green,mark=square*,mark options={fill=white}] table {re2b.data};
 \addplot[black,mark=square*,mark options={fill=white}] table {re3.data};
 \end{axis}
 \end{tikzpicture}
@@ -387,9 +387,9 @@
 Input: $r_1$, $abc$\medskip\\
 Step 1: & build derivative of $a$ and $r_1$ & $(r_2 = \textit{der}\,a\,r_1)$\smallskip\\
 Step 2: & build derivative of $b$ and $r_2$ & $(r_3 = \textit{der}\,b\,r_2)$\smallskip\\
-Step 3: & build derivative of $c$ and $r_3$ & $(r_4 = \textit{der}\,b\,r_3)$\smallskip\\
-Step 4: & the string is exhausted; test & ($\textit{nullable}(r_4)$)\\
-        & whether $r_4$ can recognise the\\
+Step 3: & build derivative of $c$ and $r_3$ & $(r_4 = \textit{der}\,c\,r_3)$\smallskip\\
+Step 4: & the string is exhausted: & $(\textit{nullable}(r_4))$\\
+        & test whether $r_4$ can recognise the\\
         & empty string\smallskip\\
 Output: & result of this test $\Rightarrow \textit{true} \,\text{or}\, \textit{false}$\\        
 \end{tabular}