diff -r df2d4bf31fcb -r 9b4503108cc0 doc/groups.dox
--- a/doc/groups.dox	Tue Sep 22 18:20:15 2015 +0200
+++ b/doc/groups.dox	Wed Oct 07 18:49:46 2015 +0200
@@ -585,7 +585,7 @@
 In addition, the graph nodes may be \e labeled, i.e. we are given two
 node labelings \f$l_1:V_1\longrightarrow L\f$ and \f$l_2:V_2\longrightarrow
 L\f$ and we require that \f$l_1(u)=l_2(f(u))\f$ holds for all nodes \f$u \in
-G\f$.
+G_1\f$.
 
 */