/*! \addtogroup gwrappers

   /*!

     The main parts of LEMON are the different graph structures, 

     generic graph algorithms, graph concepts which couple these, and 

     graph wrappers. While the previous ones are more or less clear, the 

     latter notion needs further explanation.

     Graph wrappers are graph classes which serve for considering graph 

     structures in different ways. A short example makes the notion much 

     clearer. 

     Suppose that we have an instance \c g of a directed graph

     type say \c ListGraph and an algorithm 

     \code template<typename Graph> int algorithm(const Graph&); \endcode 

     is needed to run on the reversely oriented graph. 

     It may be expensive (in time or in memory usage) to copy 

     \c g with the reverse orientation. 

     Thus, a wrapper class

     \code template<typename Graph> class RevGraphWrapper; \endcode is used. 

     The code looks as follows

     \code

     ListGraph g;

     RevGraphWrapper<ListGraph> rgw(g);

     int result=algorithm(rgw);

     \endcode

     After running the algorithm, the original graph \c g 

     remains untouched. Thus the graph wrapper used above is to consider the 

     original graph with reverse orientation. 

     This techniques gives rise to an elegant code, and 

     based on stable graph wrappers, complex algorithms can be 

     implemented easily. 

     In flow, circulation and bipartite matching problems, the residual 

     graph is of particular importance. Combining a wrapper implementing 

     this, shortest path algorithms and minimum mean cycle algorithms, 

     a range of weighted and cardinality optimization algorithms can be 

     obtained. For lack of space, for other examples, 

     the interested user is referred to the detailed documentation of graph 

     wrappers. 

     The behavior of graph wrappers can be very different. Some of them keep 

     capabilities of the original graph while in other cases this would be 

     meaningless. This means that the concepts that they are a model of depend 

     on the graph wrapper, and the wrapped graph(s). 

     If an edge of \c rgw is deleted, this is carried out by 

     deleting the corresponding edge of \c g. But for a residual 

     graph, this operation has no sense. 

     Let we stand one more example here to simplify your work. 

     wrapper class

     \code template<typename Graph> class RevGraphWrapper; \endcode 

     has constructor 

     <tt> RevGraphWrapper(Graph& _g)</tt>. 

     This means that in a situation, 

     when a <tt> const ListGraph& </tt> reference to a graph is given, 

     then it have to be instantiated with <tt>Graph=const ListGraph</tt>.

     \code

     int algorithm1(const ListGraph& g) {

     RevGraphWrapper<const ListGraph> rgw(g);

     return algorithm2(rgw);

     }

     \endcode

    */

   /*!