1.1 --- a/lemon/list_graph.h	Tue Jul 29 14:41:55 2008 +0200
     1.2 +++ b/lemon/list_graph.h	Tue Jul 29 15:06:37 2008 +0200
     1.3 @@ -842,7 +842,9 @@
     1.4        explicit Arc(int pid) { id = pid;}
     1.5  
     1.6      public:
     1.7 -      operator Edge() const { return edgeFromId(id / 2); }
     1.8 +      operator Edge() const { 
     1.9 +        return id != -1 ? edgeFromId(id / 2) : INVALID; 
    1.10 +      }
    1.11  
    1.12        Arc() {}
    1.13        Arc (Invalid) { id = -1; }