-% 5/ On size of the biggest syntheny bloc
-% 6/ On average size of syntheny blocs
-% 7/ On number of syntheny blocs.
+\subsection{Shared Synteny based Metric}
+Given two genomes abstracted as sequences of classes, it is classical
+to computes all the maximum shared synteny chains.
+
+% Attention ici, moins il y a de diff, plus le nombre est élevé
+There are then three issues with such a set of shared synteny chains:
+\begin{itemize}
+\item let $m_{Y}$ be the metric, which returns the
+length of the largest chains;
+\item let $m_{\overline{Y}}$ be the metric, which returns the
+average length of synteny chains;
+\item finally, let $m_{|Y|}$ be the metric, which returns the
+number of synteny chains.
+\end{itemize}