//     /// An empty static graph class.

 //     /// This class provides all the common features of a graph structure,

 //     /// however completely without implementations and real data structures

 //     /// behind the interface.

 //     /// All graph algorithms should compile with this class, but it will not

 //     /// run properly, of course.

 //     ///

 //     /// It can be used for checking the interface compatibility,

 //     /// or it can serve as a skeleton of a new graph structure.

 //     /// 

 //     /// Also, you will find here the full documentation of a certain graph

 //     /// feature, the documentation of a real graph imlementation

 //     /// like @ref ListGraph or

 //     /// @ref SmartGraph will just refer to this structure.

 //     ///

 //     /// \todo A pages describing the concept of concept description would

 //     /// be nice.

 //     class StaticGraph

 //     {

 //     public:

 //       /// Defalult constructor.

 //       /// Defalult constructor.

 //       ///

 //       StaticGraph() { }

 //       ///Copy consructor.

 // //       ///\todo It is not clear, what we expect from a copy constructor.

 // //       ///E.g. How to assign the nodes/edges to each other? What about maps?

 // //       StaticGraph(const StaticGraph& g) { }

 //       /// The base type of node iterators, 

 //       /// or in other words, the trivial node iterator.

 //       /// This is the base type of each node iterator,

 //       /// thus each kind of node iterator converts to this.

 //       /// More precisely each kind of node iterator should be inherited 

 //       /// from the trivial node iterator.

 //       class Node {

 //       public:

 // 	/// Default constructor

 // 	/// @warning The default constructor sets the iterator

 // 	/// to an undefined value.

 // 	Node() { }

 // 	/// Copy constructor.

 // 	/// Copy constructor.

 // 	///

 // 	Node(const Node&) { }

 // 	/// Invalid constructor \& conversion.

 // 	/// This constructor initializes the iterator to be invalid.

 // 	/// \sa Invalid for more details.

 // 	Node(Invalid) { }

 // 	/// Equality operator

 // 	/// Two iterators are equal if and only if they point to the

 // 	/// same object or both are invalid.

 // 	bool operator==(Node) const { return true; }

 // 	/// Inequality operator

 // 	/// \sa operator==(Node n)

 // 	///

 // 	bool operator!=(Node) const { return true; }

 //       };

 //       /// This iterator goes through each node.

 //       /// This iterator goes through each node.

 //       /// Its usage is quite simple, for example you can count the number

 //       /// of nodes in graph \c g of type \c Graph like this:

 //       /// \code

 //       /// int count=0;

 //       /// for (Graph::NodeIt n(g); n!=INVALID ++n) ++count;

 //       /// \endcode

 //       class NodeIt : public Node {

 //       public:

 // 	/// Default constructor

 // 	/// @warning The default constructor sets the iterator

 // 	/// to an undefined value.

 // 	NodeIt() { }

 // 	/// Copy constructor.

 // 	/// Copy constructor.

 // 	///

 // 	NodeIt(const NodeIt&) { }

 // 	/// Invalid constructor \& conversion.

 // 	/// Initialize the iterator to be invalid.

 // 	/// \sa Invalid for more details.

 // 	NodeIt(Invalid) { }

 // 	/// Sets the iterator to the first node.

 // 	/// Sets the iterator to the first node of \c g.

 // 	///

 // 	NodeIt(const StaticGraph& g) { }

 // 	/// Node -> NodeIt conversion.

 // 	/// Sets the iterator to the node of \c g pointed by the trivial 

 // 	/// iterator n.

 // 	/// This feature necessitates that each time we 

 // 	/// iterate the edge-set, the iteration order is the same.

 // 	NodeIt(const StaticGraph& g, const Node& n) { }

 // 	/// Next node.

 // 	/// Assign the iterator to the next node.

 // 	///

 // 	NodeIt& operator++() { return *this; }

 //       };

 //       /// The base type of the edge iterators.

 //       /// The base type of the edge iterators.

 //       ///

 //       class Edge {

 //       public:

 // 	/// Default constructor

 // 	/// @warning The default constructor sets the iterator

 // 	/// to an undefined value.

 // 	Edge() { }

 // 	/// Copy constructor.

 // 	/// Copy constructor.

 // 	///

 // 	Edge(const Edge&) { }

 // 	/// Initialize the iterator to be invalid.

 // 	/// Initialize the iterator to be invalid.

 // 	///

 // 	Edge(Invalid) { }

 // 	/// Equality operator

 // 	/// Two iterators are equal if and only if they point to the

 // 	/// same object or both are invalid.

 // 	bool operator==(Edge) const { return true; }

 // 	/// Inequality operator

 // 	/// \sa operator==(Node n)

 // 	///

 // 	bool operator!=(Edge) const { return true; }

 //       };

 //       /// This iterator goes trough the outgoing edges of a node.

 //       /// This iterator goes trough the \e outgoing edges of a certain node

 //       /// of a graph.

 //       /// Its usage is quite simple, for example you can count the number

 //       /// of outgoing edges of a node \c n

 //       /// in graph \c g of type \c Graph as follows.

 //       /// \code

 //       /// int count=0;

 //       /// for (Graph::OutEdgeIt e(g, n); e!=INVALID; ++e) ++count;

 //       /// \endcode

 //       class OutEdgeIt : public Edge {

 //       public:

 // 	/// Default constructor

 // 	/// @warning The default constructor sets the iterator

 // 	/// to an undefined value.

 // 	OutEdgeIt() { }

 // 	/// Copy constructor.

 // 	/// Copy constructor.

 // 	///

 // 	OutEdgeIt(const OutEdgeIt&) { }

 // 	/// Initialize the iterator to be invalid.

 // 	/// Initialize the iterator to be invalid.

 // 	///

 // 	OutEdgeIt(Invalid) { }

 // 	/// This constructor sets the iterator to first outgoing edge.

 // 	/// This constructor set the iterator to the first outgoing edge of

 // 	/// node

 // 	///@param n the node

 // 	///@param g the graph

 // 	OutEdgeIt(const StaticGraph& g, const Node& n) { }

 // 	/// Edge -> OutEdgeIt conversion

 // 	/// Sets the iterator to the value of the trivial iterator \c e.

 // 	/// This feature necessitates that each time we 

 // 	/// iterate the edge-set, the iteration order is the same.

 // 	OutEdgeIt(const StaticGraph& g, const Edge& e) { }

 // 	///Next outgoing edge

 // 	/// Assign the iterator to the next 

 // 	/// outgoing edge of the corresponding node.

 // 	OutEdgeIt& operator++() { return *this; }

 //       };

 //       /// This iterator goes trough the incoming edges of a node.

 //       /// This iterator goes trough the \e incoming edges of a certain node

 //       /// of a graph.

 //       /// Its usage is quite simple, for example you can count the number

 //       /// of outgoing edges of a node \c n

 //       /// in graph \c g of type \c Graph as follows.

 //       /// \code

 //       /// int count=0;

 //       /// for(Graph::InEdgeIt e(g, n); e!=INVALID; ++e) ++count;

 //       /// \endcode

 //       class InEdgeIt : public Edge {

 //       public:

 // 	/// Default constructor

 // 	/// @warning The default constructor sets the iterator

 // 	/// to an undefined value.

 // 	InEdgeIt() { }

 // 	/// Copy constructor.

 // 	/// Copy constructor.

 // 	///

 // 	InEdgeIt(const InEdgeIt&) { }

 // 	/// Initialize the iterator to be invalid.

 // 	/// Initialize the iterator to be invalid.

 // 	///

 // 	InEdgeIt(Invalid) { }

 // 	/// This constructor sets the iterator to first incoming edge.

 // 	/// This constructor set the iterator to the first incoming edge of

 // 	/// node

 // 	///@param n the node

 // 	///@param g the graph

 // 	InEdgeIt(const StaticGraph& g, const Node& n) { }

 // 	/// Edge -> InEdgeIt conversion

 // 	/// Sets the iterator to the value of the trivial iterator \c e.

 // 	/// This feature necessitates that each time we 

 // 	/// iterate the edge-set, the iteration order is the same.

 // 	InEdgeIt(const StaticGraph& g, const Edge& n) { }

 // 	/// Next incoming edge

 // 	/// Assign the iterator to the next inedge of the corresponding node.

 // 	///

 // 	InEdgeIt& operator++() { return *this; }

 //       };

 //       /// This iterator goes through each edge.

 //       /// This iterator goes through each edge of a graph.

 //       /// Its usage is quite simple, for example you can count the number

 //       /// of edges in a graph \c g of type \c Graph as follows:

 //       /// \code

 //       /// int count=0;

 //       /// for(Graph::EdgeIt e(g); e!=INVALID; ++e) ++count;

 //       /// \endcode

 //       class EdgeIt : public Edge {

 //       public:

 // 	/// Default constructor

 // 	/// @warning The default constructor sets the iterator

 // 	/// to an undefined value.

 // 	EdgeIt() { }

 // 	/// Copy constructor.

 // 	/// Copy constructor.

 // 	///

 // 	EdgeIt(const EdgeIt&) { }

 // 	/// Initialize the iterator to be invalid.

 // 	/// Initialize the iterator to be invalid.

 // 	///

 // 	EdgeIt(Invalid) { }

 // 	/// This constructor sets the iterator to first edge.

 // 	/// This constructor set the iterator to the first edge of

 // 	/// node

 // 	///@param g the graph

 // 	EdgeIt(const StaticGraph& g) { }

 // 	/// Edge -> EdgeIt conversion

 // 	/// Sets the iterator to the value of the trivial iterator \c e.

 // 	/// This feature necessitates that each time we 

 // 	/// iterate the edge-set, the iteration order is the same.

 // 	EdgeIt(const StaticGraph&, const Edge&) { } 

 //     	///Next edge

 // 	/// Assign the iterator to the next 

 // 	/// edge of the corresponding node.

 // 	EdgeIt& operator++() { return *this; }

 //       };

 //       ///Gives back the target node of an edge.

 //       ///Gives back the target node of an edge.

 //       ///

 //       Node target(Edge) const { return INVALID; }

 //       ///Gives back the source node of an edge.

 //       ///Gives back the source node of an edge.

 //       ///

 //       Node source(Edge) const { return INVALID; }

 //       /// Read write map of the nodes to type \c T.

 //       /// \ingroup concept

 //       /// ReadWrite map of the nodes to type \c T.

 //       /// \sa Reference

 //       /// \warning Making maps that can handle bool type (NodeMap<bool>)

 //       /// needs some extra attention!

 //       template<class T> 

 //       class NodeMap : public ReadWriteMap< Node, T >

 //       {

 //       public:

 // 	///\e

 // 	NodeMap(const StaticGraph&) { }

 // 	///\e

 // 	NodeMap(const StaticGraph&, T) { }

 // 	///Copy constructor

 // 	NodeMap(const NodeMap&) { }

 // 	///Assignment operator

 // 	NodeMap& operator=(const NodeMap&) { return *this; }

 // 	// \todo fix this concept

 //       };

 //       /// Read write map of the edges to type \c T.

 //       /// \ingroup concept

 //       ///Reference map of the edges to type \c T.

 //       /// \sa Reference

 //       /// \warning Making maps that can handle bool type (EdgeMap<bool>)

 //       /// needs some extra attention!

 //       template<class T> 

 //       class EdgeMap : public ReadWriteMap<Edge,T>

 //       {

 //       public:

 // 	///\e

 // 	EdgeMap(const StaticGraph&) { }

 // 	///\e

 // 	EdgeMap(const StaticGraph&, T) { }

 // 	///Copy constructor

 // 	EdgeMap(const EdgeMap&) { }

 // 	///Assignment operator

 // 	EdgeMap& operator=(const EdgeMap&) { return *this; }

 // 	// \todo fix this concept    

 //       };

 //     };

 //     /// An empty non-static graph class.

 //     /// This class provides everything that \ref StaticGraph

 //     /// with additional functionality which enables to build a

 //     /// graph from scratch.

 //     class ExtendableGraph : public StaticGraph

 //     {

 //     public:

 //       /// Defalult constructor.

 //       /// Defalult constructor.

 //       ///

 //       ExtendableGraph() { }

 //       ///Add a new node to the graph.

 //       /// \return the new node.

 //       ///

 //       Node addNode() { return INVALID; }

 //       ///Add a new edge to the graph.

 //       ///Add a new edge to the graph with source node \c s

 //       ///and target node \c t.

 //       ///\return the new edge.

 //       Edge addEdge(Node s, Node t) { return INVALID; }

 //       /// Resets the graph.

 //       /// This function deletes all edges and nodes of the graph.

 //       /// It also frees the memory allocated to store them.

 //       /// \todo It might belong to \ref ErasableGraph.

 //       void clear() { }

 //     };

 //     /// An empty erasable graph class.

 //     /// This class is an extension of \ref ExtendableGraph. It also makes it

 //     /// possible to erase edges or nodes.

 //     class ErasableGraph : public ExtendableGraph

 //     {

 //     public:

 //       /// Defalult constructor.

 //       /// Defalult constructor.

 //       ///

 //       ErasableGraph() { }

 //       /// Deletes a node.

 //       /// Deletes node \c n node.

 //       ///

 //       void erase(Node n) { }

 //       /// Deletes an edge.

 //       /// Deletes edge \c e edge.

 //       ///

 //       void erase(Edge e) { }

 //     };

     /************* New GraphBase stuff **************/

     /// A minimal GraphBase concept

     /// This class describes a minimal concept which can be extended to a

     /// full-featured graph with \ref GraphFactory.

     class GraphBase {

     public:

       GraphBase() {}

       /// \bug Should we demand that Node and Edge be subclasses of the

       /// Graph class???

       typedef GraphItem<'n'> Node;

       typedef GraphItem<'e'> Edge;

 //       class Node : public BaseGraphItem<'n'> {};

 //       class Edge : public BaseGraphItem<'e'> {};

       // Graph operation

       void firstNode(Node &n) const { }

       void firstEdge(Edge &e) const { }

       void firstOutEdge(Edge &e, Node) const { }

       void firstInEdge(Edge &e, Node) const { }

       void nextNode(Node &n) const { }

       void nextEdge(Edge &e) const { }

       // Question: isn't it reasonable if this methods have a Node

       // parameter? Like this:

       // Edge& nextOut(Edge &e, Node) const { return e; }

       void nextOutEdge(Edge &e) const { }

       void nextInEdge(Edge &e) const { }

       Node target(Edge) const { return Node(); }

       Node source(Edge) const { return Node(); }

       // Do we need id, nodeNum, edgeNum and co. in this basic graphbase

       // concept?

       // Maps.

       //

       // We need a special slimer concept which does not provide maps (it

       // wouldn't be strictly slimer, cause for map-factory id() & friends

       // a required...)

       template<typename T>

       class NodeMap : public GraphMap<GraphBase, Node, T> {};

       template<typename T>

       class EdgeMap : public GraphMap<GraphBase, Node, T> {};

     };