diff --git a/cw/cw.tex b/cw/cw.tex
index b157e43..27748ff 100644
--- a/cw/cw.tex
+++ b/cw/cw.tex
@@ -190,8 +190,16 @@
 	$$\begin{cases}
 		s  = r - h  \times a \text{ mod } q\\
 		s' = r - h' \times a \text{ mod } q
+	\end{cases} \iff
+	\begin{cases}
+		r = s + h \times a \\
+		a = \frac{s' - s}{h - h'} \land h \ne h'
 	\end{cases}
 	$$
+	therefor Alice private key $a$ is:
+	$$
+		a = \frac{s' - s}{h - h'}
+	$$
 
 	\section*{7}
 	\subsection*{7.1}