/// This error represents problems in the initialization

     /// This error represents problems in the initialization

     /// of the parameters of the algorithms.

     /// of the parameters of the algorithms.

     class UninitializedParameter : public lemon::UninitializedParameter {

     class UninitializedParameter : public lemon::UninitializedParameter {

     public:

     public:

       virtual const char* what() const throw() 

       virtual const char* what() const throw() 

 	return "lemon::DfsVisit::UninitializedParameter";

 	return "lemon::DfsVisit::UninitializedParameter";

       }

       }

     };

     };

     typedef _Traits Traits;

     typedef _Traits Traits;