diff --git a/src/CommonSOG.h b/src/CommonSOG.h
index c1480c461b27edfb91c657dacd60bbd44d5a79c0..229e5b87946f0e19a4b614db2b05b08c85b1c769 100644
--- a/src/CommonSOG.h
+++ b/src/CommonSOG.h
@@ -12,7 +12,9 @@ class LDDState;
 typedef pair<LDDState *, MDD> couple;
 typedef pair<couple, Set> Pair;
 typedef stack<Pair> pile;
+
 class LDDGraph;
+
 class CommonSOG
 {
     public: