///\brief Demonstrating the basic concepts and fetures of LEMON

 ///\brief Simple "Hello World!" program for LEMON.

 /// This program is intended to be a "Hello World!" program that shows

 /// Simple "Hello World!" program for LEMON.

 /// the very basic notions of LEMON: \ref graphs "graphs" and

 /// \ref maps "maps".

 ///

   // Convenience type definitions

   typedef lemon::ListDigraph Graph;

   typedef lemon::ListDigraph Digraph;

   Graph g;

   typedef Digraph::Node Node;

   typedef Digraph::Arc Arc;

   typedef Digraph::NodeIt NodeIt;

   typedef Digraph::ArcIt ArcIt;

   typedef Digraph::ArcMap<int> LengthMap;

   using lemon::INVALID;

   // Create a directed graph

   Graph::Node u = g.addNode();

   Digraph g;

   Graph::Node v = g.addNode();

   Graph::Arc  e = g.addArc(u, v);

   // Add nodes to the digraph

   std::cout << "Hello World! This is LEMON library here." << std::endl;

   Node v1 = g.addNode();

   std::cout << "We have a directed graph with "

   Node v2 = g.addNode();

             << countNodes(g) << " nodes and "

   Node v3 = g.addNode();

             << countArcs(g) << " arc." << std::endl;

   Node v4 = g.addNode();

   // Add arcs to the digraph

   Arc v1_v2 = g.addArc(v1, v2);

   Arc v1_v3 = g.addArc(v1, v3);

   Arc v2_v3 = g.addArc(v2, v3);

   Arc v2_v4 = g.addArc(v2, v4);

   Arc v3_v4 = g.addArc(v3, v4);

   // Create an arc map (length)

   LengthMap length(g);

   // Set the length of each arc

   length[v1_v2]  = 10;

   length[v1_v3]  = 20;

   length[v2_v3] = 5;

   length[v2_v4] = 25;

   length[v3_v4] = 10;

   // Welcome message

   std::cout << "Hello World!" << std::endl;

   std::cout << "This is LEMON library here. We have a direceted graph.";

   std::cout << std::endl << std::endl;

   // Iterate through the nodes and print their IDs

   std::cout << "Nodes:";

   for (NodeIt n(g); n != INVALID; ++n)

     std::cout << " " << g.id(n);

   std::cout << std::endl;

   // Iterate through the arcs and print the IDs of their

   // source and target nodes

   std::cout << "Arcs:";

   for (ArcIt a(g); a != INVALID; ++a)

     std::cout << " (" << g.id(g.source(a)) << ","

               << g.id(g.target(a)) << ")";

   std::cout << std::endl << std::endl;

   // Iterate through the arcs and print their length

   std::cout << "There is a map on the arcs (length):" << std::endl;

   std::cout << std::endl;

   for (ArcIt a(g); a != INVALID; ++a)

     std::cout << "length(" << g.id(g.source(a)) << ","

               << g.id(g.target(a)) << ")=" << length[a] << std::endl;

   std::cout << std::endl;