/** @defgroup gwrappers Wrapper Classes for Graphs \brief This group contains several wrapper classes for graphs @ingroup graphs The main parts of LEMON are the different graph structures, generic graph algorithms, graph concepts which couple these, and graph wrappers. While the previous notions are more or less clear, the latter one needs further explanation. Graph wrappers are graph classes which serve for considering graph structures in different ways. A short example makes this much clearer. Suppose that we have an instance \c g of a directed graph type say ListGraph and an algorithm \code template int algorithm(const Graph&); \endcode is needed to run on the reversed oriented graph. It may be expensive (in time or in memory usage) to copy \c g with the reversed orientation. In this case, a wrapper class is used, which (according to LEMON graph concepts) works as a graph. The wrapper uses the original graph structure and graph operations when methods of the reversed oriented graph are called. This means that the wrapper have minor memory usage, and do not perform sophisticated algorithmic actions. The purpose of it is to give a tool for the cases when a graph have to be used in a specific alteration. If this alteration is obtained by a usual construction like filtering the edge-set or considering a new orientation, then a wrapper is worthwhile to use. To come back to the reversed oriented graph, in this situation \code template class RevGraphWrapper; \endcode template class can be used. The code looks as follows \code ListGraph g; RevGraphWrapper rgw(g); int result=algorithm(rgw); \endcode After running the algorithm, the original graph \c g is untouched. 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 other examples, the interested user is referred to the detailed documentation of particular 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 models 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, thus the wrapper modifies the original graph. But for a residual graph, this operation has no sense. Let us stand one more example here to simplify your work. RevGraphWrapper has constructor \code RevGraphWrapper(Graph& _g); \endcode This means that in a situation, when a const ListGraph& reference to a graph is given, then it have to be instantiated with Graph=const ListGraph. \code int algorithm1(const ListGraph& g) { RevGraphWrapper rgw(g); return algorithm2(rgw); } \endcode */