diff -r 5289afbdb720 -r be025fc1b13d lemon/list_graph.h
--- a/lemon/list_graph.h	Thu Jun 09 09:46:34 2005 +0000
+++ b/lemon/list_graph.h	Thu Jun 09 09:47:51 2005 +0000
@@ -457,6 +457,13 @@
 	exit(1);
       }
 
+      ///\bug What is this used for?
+      ///
+      virtual void build() {}
+      ///\bug What is this used for?
+      ///
+      virtual void clear() {}
+
       void regist(ListGraph &_g) {
 	g=&_g;
 	AlterationNotifier<Node>::ObserverBase::
@@ -517,13 +524,14 @@
     ///
     ///\todo This function might be called undo().
       void restore() {
+	ListGraph &old_g=*g;
 	deregist();
 	while(!added_edges.empty()) {
-	  g->erase(added_edges.front());
+	  old_g.erase(added_edges.front());
 	  added_edges.pop_front();
 	}
  	while(!added_nodes.empty()) {
-	  g->erase(added_nodes.front());
+	  old_g.erase(added_nodes.front());
 	  added_nodes.pop_front();
 	}
       }