+
+We compute the core genome as follow.
+Each genome is projected according to $\pi$. We then consider the
+intersection of all the projected genomes which are considered as sets of genes
+and not as sequences of genes.
+This results as the set of all the class $\dot{x}$
+such that each genome has an gene $x$ in $\dot{x}$.
+The pan genome is computed similarly: the union of all the
+projected genomes in computed here.
+