diff --git a/lemon/smart_graph.h b/lemon/smart_graph.h
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--- /dev/null
+++ b/lemon/smart_graph.h
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+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2008
+ * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
+ * (Egervary Research Group on Combinatorial Optimization, EGRES).
+ *
+ * Permission to use, modify and distribute this software is granted
+ * provided that this copyright notice appears in all copies. For
+ * precise terms see the accompanying LICENSE file.
+ *
+ * This software is provided "AS IS" with no warranty of any kind,
+ * express or implied, and with no claim as to its suitability for any
+ * purpose.
+ *
+ */
+
+#ifndef LEMON_SMART_GRAPH_H
+#define LEMON_SMART_GRAPH_H
+
+///\ingroup graphs
+///\file
+///\brief SmartDigraph and SmartGraph classes.
+
+#include <vector>
+
+#include <lemon/bits/invalid.h>
+
+#include <lemon/bits/base_extender.h>
+#include <lemon/bits/graph_extender.h>
+
+#include <lemon/bits/utility.h>
+#include <lemon/error.h>
+
+#include <lemon/bits/graph_extender.h>
+
+namespace lemon {
+
+  class SmartDigraph;
+  ///Base of SmartDigraph
+
+  ///Base of SmartDigraph
+  ///
+  class SmartDigraphBase {
+  protected:
+
+    struct NodeT 
+    {
+      int first_in, first_out;      
+      NodeT() {}
+    };
+    struct ArcT 
+    {
+      int target, source, next_in, next_out;      
+      ArcT() {}  
+    };
+
+    std::vector<NodeT> nodes;
+    std::vector<ArcT> arcs;
+        
+  public:
+
+    typedef SmartDigraphBase Graph;
+
+    class Node;
+    class Arc;
+
+  public:
+
+    SmartDigraphBase() : nodes(), arcs() { }
+    SmartDigraphBase(const SmartDigraphBase &_g) 
+      : nodes(_g.nodes), arcs(_g.arcs) { }
+    
+    typedef True NodeNumTag;
+    typedef True ArcNumTag;
+
+    int nodeNum() const { return nodes.size(); }
+    int arcNum() const { return arcs.size(); }
+
+    int maxNodeId() const { return nodes.size()-1; }
+    int maxArcId() const { return arcs.size()-1; }
+
+    Node addNode() {
+      int n = nodes.size();     
+      nodes.push_back(NodeT());
+      nodes[n].first_in = -1;
+      nodes[n].first_out = -1;
+      return Node(n);
+    }
+    
+    Arc addArc(Node u, Node v) {
+      int n = arcs.size(); 
+      arcs.push_back(ArcT());
+      arcs[n].source = u._id; 
+      arcs[n].target = v._id;
+      arcs[n].next_out = nodes[u._id].first_out;
+      arcs[n].next_in = nodes[v._id].first_in;
+      nodes[u._id].first_out = nodes[v._id].first_in = n;
+
+      return Arc(n);
+    }
+
+    void clear() {
+      arcs.clear();
+      nodes.clear();
+    }
+
+    Node source(Arc a) const { return Node(arcs[a._id].source); }
+    Node target(Arc a) const { return Node(arcs[a._id].target); }
+
+    static int id(Node v) { return v._id; }
+    static int id(Arc a) { return a._id; }
+
+    static Node nodeFromId(int id) { return Node(id);}
+    static Arc arcFromId(int id) { return Arc(id);}
+
+    class Node {
+      friend class SmartDigraphBase;
+      friend class SmartDigraph;
+
+    protected:
+      int _id;
+      explicit Node(int id) : _id(id) {}
+    public:
+      Node() {}
+      Node (Invalid) : _id(-1) {}
+      bool operator==(const Node i) const {return _id == i._id;}
+      bool operator!=(const Node i) const {return _id != i._id;}
+      bool operator<(const Node i) const {return _id < i._id;}
+    };
+    
+
+    class Arc {
+      friend class SmartDigraphBase;
+      friend class SmartDigraph;
+
+    protected:
+      int _id;
+      explicit Arc(int id) : _id(id) {}
+    public:
+      Arc() { }
+      Arc (Invalid) : _id(-1) {}
+      bool operator==(const Arc i) const {return _id == i._id;}
+      bool operator!=(const Arc i) const {return _id != i._id;}
+      bool operator<(const Arc i) const {return _id < i._id;}
+    };
+
+    void first(Node& node) const {
+      node._id = nodes.size() - 1;
+    }
+
+    static void next(Node& node) {
+      --node._id;
+    }
+
+    void first(Arc& arc) const {
+      arc._id = arcs.size() - 1;
+    }
+
+    static void next(Arc& arc) {
+      --arc._id;
+    }
+
+    void firstOut(Arc& arc, const Node& node) const {
+      arc._id = nodes[node._id].first_out;
+    }
+
+    void nextOut(Arc& arc) const {
+      arc._id = arcs[arc._id].next_out;
+    }
+
+    void firstIn(Arc& arc, const Node& node) const {
+      arc._id = nodes[node._id].first_in;
+    }
+    
+    void nextIn(Arc& arc) const {
+      arc._id = arcs[arc._id].next_in;
+    }
+
+  };
+
+  typedef DigraphExtender<SmartDigraphBase> ExtendedSmartDigraphBase;
+
+  ///\ingroup graphs
+  ///
+  ///\brief A smart directed graph class.
+  ///
+  ///This is a simple and fast digraph implementation.
+  ///It is also quite memory efficient, but at the price
+  ///that <b> it does support only limited (only stack-like)
+  ///node and arc deletions</b>.
+  ///It conforms to the \ref concepts::Digraph "Digraph concept" with
+  ///an important extra feature that its maps are real \ref
+  ///concepts::ReferenceMap "reference map"s.
+  ///
+  ///\sa concepts::Digraph.
+  ///
+  ///\author Alpar Juttner
+  class SmartDigraph : public ExtendedSmartDigraphBase {
+  public:
+
+    typedef ExtendedSmartDigraphBase Parent;
+
+  private:
+
+    ///SmartDigraph is \e not copy constructible. Use DigraphCopy() instead.
+
+    ///SmartDigraph is \e not copy constructible. Use DigraphCopy() instead.
+    ///
+    SmartDigraph(const SmartDigraph &) : ExtendedSmartDigraphBase() {};
+    ///\brief Assignment of SmartDigraph to another one is \e not allowed.
+    ///Use DigraphCopy() instead.
+
+    ///Assignment of SmartDigraph to another one is \e not allowed.
+    ///Use DigraphCopy() instead.
+    void operator=(const SmartDigraph &) {}
+
+  public:
+    
+    /// Constructor
+    
+    /// Constructor.
+    ///
+    SmartDigraph() {};
+    
+    ///Add a new node to the digraph.
+    
+    /// \return the new node.
+    ///
+    Node addNode() { return Parent::addNode(); }
+    
+    ///Add a new arc to the digraph.
+    
+    ///Add a new arc to the digraph with source node \c s
+    ///and target node \c t.
+    ///\return the new arc.
+    Arc addArc(const Node& s, const Node& t) { 
+      return Parent::addArc(s, t); 
+    }
+
+    /// \brief Using this it is possible to avoid the superfluous memory
+    /// allocation.
+
+    /// Using this it is possible to avoid the superfluous memory
+    /// allocation: if you know that the digraph you want to build will
+    /// be very large (e.g. it will contain millions of nodes and/or arcs)
+    /// then it is worth reserving space for this amount before starting
+    /// to build the digraph.
+    /// \sa reserveArc
+    void reserveNode(int n) { nodes.reserve(n); };
+
+    /// \brief Using this it is possible to avoid the superfluous memory
+    /// allocation.
+
+    /// Using this it is possible to avoid the superfluous memory
+    /// allocation: if you know that the digraph you want to build will
+    /// be very large (e.g. it will contain millions of nodes and/or arcs)
+    /// then it is worth reserving space for this amount before starting
+    /// to build the digraph.
+    /// \sa reserveNode
+    void reserveArc(int m) { arcs.reserve(m); };
+
+    ///Clear the digraph.
+    
+    ///Erase all the nodes and arcs from the digraph.
+    ///
+    void clear() {
+      Parent::clear();
+    }
+
+    ///Split a node.
+    
+    ///This function splits a node. First a new node is added to the digraph,
+    ///then the source of each outgoing arc of \c n is moved to this new node.
+    ///If \c connect is \c true (this is the default value), then a new arc
+    ///from \c n to the newly created node is also added.
+    ///\return The newly created node.
+    ///
+    ///\note The <tt>Arc</tt>s
+    ///referencing a moved arc remain
+    ///valid. However <tt>InArc</tt>'s and <tt>OutArc</tt>'s
+    ///may be invalidated.
+    ///\warning This functionality cannot be used together with the Snapshot
+    ///feature.
+    ///\todo It could be implemented in a bit faster way.
+    Node split(Node n, bool connect = true)
+    {
+      Node b = addNode();
+      nodes[b._id].first_out=nodes[n._id].first_out;
+      nodes[n._id].first_out=-1;
+      for(int i=nodes[b._id].first_out;i!=-1;i++) arcs[i].source=b._id;
+      if(connect) addArc(n,b);
+      return b;
+    }
+
+  public:
+    
+    class Snapshot;
+
+  protected:
+
+    void restoreSnapshot(const Snapshot &s)
+    {
+      while(s.arc_num<arcs.size()) {
+        Arc arc = arcFromId(arcs.size()-1);
+	Parent::notifier(Arc()).erase(arc);
+	nodes[arcs.back().source].first_out=arcs.back().next_out;
+	nodes[arcs.back().target].first_in=arcs.back().next_in;
+	arcs.pop_back();
+      }
+      while(s.node_num<nodes.size()) {
+        Node node = nodeFromId(nodes.size()-1);
+	Parent::notifier(Node()).erase(node);
+	nodes.pop_back();
+      }
+    }    
+
+  public:
+
+    ///Class to make a snapshot of the digraph and to restrore to it later.
+
+    ///Class to make a snapshot of the digraph and to restrore to it later.
+    ///
+    ///The newly added nodes and arcs can be removed using the
+    ///restore() function.
+    ///\note After you restore a state, you cannot restore
+    ///a later state, in other word you cannot add again the arcs deleted
+    ///by restore() using another one Snapshot instance.
+    ///
+    ///\warning If you do not use correctly the snapshot that can cause
+    ///either broken program, invalid state of the digraph, valid but
+    ///not the restored digraph or no change. Because the runtime performance
+    ///the validity of the snapshot is not stored.
+    class Snapshot 
+    {
+      SmartDigraph *_graph;
+    protected:
+      friend class SmartDigraph;
+      unsigned int node_num;
+      unsigned int arc_num;
+    public:
+      ///Default constructor.
+      
+      ///Default constructor.
+      ///To actually make a snapshot you must call save().
+      ///
+      Snapshot() : _graph(0) {}
+      ///Constructor that immediately makes a snapshot
+      
+      ///This constructor immediately makes a snapshot of the digraph.
+      ///\param _g The digraph we make a snapshot of.
+      Snapshot(SmartDigraph &graph) : _graph(&graph) {
+	node_num=_graph->nodes.size();
+	arc_num=_graph->arcs.size();
+      }
+
+      ///Make a snapshot.
+
+      ///Make a snapshot of the digraph.
+      ///
+      ///This function can be called more than once. In case of a repeated
+      ///call, the previous snapshot gets lost.
+      ///\param _g The digraph we make the snapshot of.
+      void save(SmartDigraph &graph) 
+      {
+	_graph=&graph;
+	node_num=_graph->nodes.size();
+	arc_num=_graph->arcs.size();
+      }
+
+      ///Undo the changes until a snapshot.
+      
+      ///Undo the changes until a snapshot created by save().
+      ///
+      ///\note After you restored a state, you cannot restore
+      ///a later state, in other word you cannot add again the arcs deleted
+      ///by restore().
+      void restore()
+      {
+	_graph->restoreSnapshot(*this);
+      }
+    };
+  };
+
+
+  class SmartGraphBase {
+
+  protected:
+
+    struct NodeT {
+      int first_out;
+    };
+ 
+    struct ArcT {
+      int target;
+      int next_out;
+    };
+
+    std::vector<NodeT> nodes;
+    std::vector<ArcT> arcs;
+
+    int first_free_arc;
+    
+  public:
+    
+    typedef SmartGraphBase Digraph;
+
+    class Node;
+    class Arc;
+    class Edge;
+    
+    class Node {
+      friend class SmartGraphBase;
+    protected:
+
+      int _id;
+      explicit Node(int id) { _id = id;}
+
+    public:
+      Node() {}
+      Node (Invalid) { _id = -1; }
+      bool operator==(const Node& node) const {return _id == node._id;}
+      bool operator!=(const Node& node) const {return _id != node._id;}
+      bool operator<(const Node& node) const {return _id < node._id;}
+    };
+
+    class Edge {
+      friend class SmartGraphBase;
+    protected:
+
+      int _id;
+      explicit Edge(int id) { _id = id;}
+
+    public:
+      Edge() {}
+      Edge (Invalid) { _id = -1; }
+      bool operator==(const Edge& arc) const {return _id == arc._id;}
+      bool operator!=(const Edge& arc) const {return _id != arc._id;}
+      bool operator<(const Edge& arc) const {return _id < arc._id;}
+    };
+
+    class Arc {
+      friend class SmartGraphBase;
+    protected:
+
+      int _id;
+      explicit Arc(int id) { _id = id;}
+
+    public:
+      operator Edge() const { return edgeFromId(_id / 2); }
+
+      Arc() {}
+      Arc (Invalid) { _id = -1; }
+      bool operator==(const Arc& arc) const {return _id == arc._id;}
+      bool operator!=(const Arc& arc) const {return _id != arc._id;}
+      bool operator<(const Arc& arc) const {return _id < arc._id;}
+    };
+
+
+
+    SmartGraphBase()
+      : nodes(), arcs() {}
+
+    
+    int maxNodeId() const { return nodes.size()-1; } 
+    int maxEdgeId() const { return arcs.size() / 2 - 1; }
+    int maxArcId() const { return arcs.size()-1; }
+
+    Node source(Arc e) const { return Node(arcs[e._id ^ 1].target); }
+    Node target(Arc e) const { return Node(arcs[e._id].target); }
+
+    Node source(Edge e) const { return Node(arcs[2 * e._id].target); }
+    Node target(Edge e) const { return Node(arcs[2 * e._id + 1].target); }
+
+    static bool direction(Arc e) {
+      return (e._id & 1) == 1;
+    }
+
+    static Arc direct(Edge e, bool d) {
+      return Arc(e._id * 2 + (d ? 1 : 0));
+    }
+
+    void first(Node& node) const { 
+      node._id = nodes.size() - 1;
+    }
+
+    void next(Node& node) const {
+      --node._id;
+    }
+
+    void first(Arc& arc) const { 
+      arc._id = arcs.size() - 1;
+    }
+
+    void next(Arc& arc) const {
+      --arc._id;
+    }
+
+    void first(Edge& arc) const { 
+      arc._id = arcs.size() / 2 - 1;
+    }
+
+    void next(Edge& arc) const {
+      --arc._id;
+    }
+
+    void firstOut(Arc &arc, const Node& v) const {
+      arc._id = nodes[v._id].first_out;
+    }
+    void nextOut(Arc &arc) const {
+      arc._id = arcs[arc._id].next_out;
+    }
+
+    void firstIn(Arc &arc, const Node& v) const {
+      arc._id = ((nodes[v._id].first_out) ^ 1);
+      if (arc._id == -2) arc._id = -1;
+    }
+    void nextIn(Arc &arc) const {
+      arc._id = ((arcs[arc._id ^ 1].next_out) ^ 1);
+      if (arc._id == -2) arc._id = -1;
+    }
+
+    void firstInc(Edge &arc, bool& d, const Node& v) const {
+      int de = nodes[v._id].first_out;
+      if (de != -1) {
+        arc._id = de / 2;
+        d = ((de & 1) == 1);
+      } else {
+        arc._id = -1;
+        d = true;
+      }
+    }
+    void nextInc(Edge &arc, bool& d) const {
+      int de = (arcs[(arc._id * 2) | (d ? 1 : 0)].next_out);
+      if (de != -1) {
+        arc._id = de / 2;
+        d = ((de & 1) == 1);
+      } else {
+        arc._id = -1;
+        d = true;      
+      }
+    }
+    
+    static int id(Node v) { return v._id; }
+    static int id(Arc e) { return e._id; }
+    static int id(Edge e) { return e._id; }
+
+    static Node nodeFromId(int id) { return Node(id);}
+    static Arc arcFromId(int id) { return Arc(id);}
+    static Edge edgeFromId(int id) { return Edge(id);}
+
+    Node addNode() {     
+      int n = nodes.size();
+      nodes.push_back(NodeT());
+      nodes[n].first_out = -1;
+      
+      return Node(n);
+    }
+    
+    Edge addArc(Node u, Node v) {
+      int n = arcs.size();
+      arcs.push_back(ArcT());
+      arcs.push_back(ArcT());
+      
+      arcs[n].target = u._id;
+      arcs[n | 1].target = v._id;
+
+      arcs[n].next_out = nodes[v._id].first_out;
+      nodes[v._id].first_out = n;
+
+      arcs[n | 1].next_out = nodes[u._id].first_out;	
+      nodes[u._id].first_out = (n | 1);
+
+      return Edge(n / 2);
+    }
+    
+    void clear() {
+      arcs.clear();
+      nodes.clear();
+    }
+
+  };
+
+  typedef GraphExtender<SmartGraphBase> ExtendedSmartGraphBase;
+
+  /// \ingroup graphs
+  ///
+  /// \brief A smart undirected graph class.
+  ///
+  /// This is a simple and fast graph implementation.
+  /// It is also quite memory efficient, but at the price
+  /// that <b> it does support only limited (only stack-like)
+  /// node and arc deletions</b>.
+  /// Except from this it conforms to 
+  /// the \ref concepts::Graph "Graph concept".
+  ///
+  /// It also has an
+  /// important extra feature that
+  /// its maps are real \ref concepts::ReferenceMap "reference map"s.
+  ///
+  /// \sa concepts::Graph.
+  ///
+  class SmartGraph : public ExtendedSmartGraphBase {
+  private:
+
+    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
+
+    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
+    ///
+    SmartGraph(const SmartGraph &) : ExtendedSmartGraphBase() {};
+
+    ///\brief Assignment of SmartGraph to another one is \e not allowed.
+    ///Use GraphCopy() instead.
+
+    ///Assignment of SmartGraph to another one is \e not allowed.
+    ///Use GraphCopy() instead.
+    void operator=(const SmartGraph &) {}
+
+  public:
+
+    typedef ExtendedSmartGraphBase Parent;
+
+    /// Constructor
+    
+    /// Constructor.
+    ///
+    SmartGraph() {}
+
+    ///Add a new node to the graph.
+    
+    /// \return the new node.
+    ///
+    Node addNode() { return Parent::addNode(); }
+    
+    ///Add a new edge to the graph.
+    
+    ///Add a new edge to the graph with node \c s
+    ///and \c t.
+    ///\return the new edge.
+    Edge addEdge(const Node& s, const Node& t) { 
+      return Parent::addArc(s, t); 
+    }
+
+    ///Clear the graph.
+    
+    ///Erase all the nodes and edges from the graph.
+    ///
+    void clear() {
+      Parent::clear();
+    }
+
+  public:
+    
+    class Snapshot;
+
+  protected:
+
+    void saveSnapshot(Snapshot &s)
+    {
+      s._graph = this;
+      s.node_num = nodes.size();
+      s.arc_num = arcs.size();
+    }
+
+    void restoreSnapshot(const Snapshot &s)
+    {
+      while(s.arc_num<arcs.size()) {
+        int n=arcs.size()-1;
+        Edge arc=edgeFromId(n/2);
+	Parent::notifier(Edge()).erase(arc);
+        std::vector<Arc> dir;
+        dir.push_back(arcFromId(n));
+        dir.push_back(arcFromId(n-1));
+	Parent::notifier(Arc()).erase(dir);
+	nodes[arcs[n].target].first_out=arcs[n].next_out;
+	nodes[arcs[n-1].target].first_out=arcs[n-1].next_out;
+	arcs.pop_back();
+	arcs.pop_back();
+      }
+      while(s.node_num<nodes.size()) {
+        int n=nodes.size()-1;
+        Node node = nodeFromId(n);
+	Parent::notifier(Node()).erase(node);
+	nodes.pop_back();
+      }
+    }    
+
+  public:
+
+    ///Class to make a snapshot of the digraph and to restrore to it later.
+
+    ///Class to make a snapshot of the digraph and to restrore to it later.
+    ///
+    ///The newly added nodes and arcs can be removed using the
+    ///restore() function.
+    ///
+    ///\note After you restore a state, you cannot restore
+    ///a later state, in other word you cannot add again the arcs deleted
+    ///by restore() using another one Snapshot instance.
+    ///
+    ///\warning If you do not use correctly the snapshot that can cause
+    ///either broken program, invalid state of the digraph, valid but
+    ///not the restored digraph or no change. Because the runtime performance
+    ///the validity of the snapshot is not stored.
+    class Snapshot 
+    {
+      SmartGraph *_graph;
+    protected:
+      friend class SmartGraph;
+      unsigned int node_num;
+      unsigned int arc_num;
+    public:
+      ///Default constructor.
+      
+      ///Default constructor.
+      ///To actually make a snapshot you must call save().
+      ///
+      Snapshot() : _graph(0) {}
+      ///Constructor that immediately makes a snapshot
+      
+      ///This constructor immediately makes a snapshot of the digraph.
+      ///\param g The digraph we make a snapshot of.
+      Snapshot(SmartGraph &graph) {
+        graph.saveSnapshot(*this);
+      }
+
+      ///Make a snapshot.
+
+      ///Make a snapshot of the graph.
+      ///
+      ///This function can be called more than once. In case of a repeated
+      ///call, the previous snapshot gets lost.
+      ///\param g The digraph we make the snapshot of.
+      void save(SmartGraph &graph) 
+      {
+        graph.saveSnapshot(*this);
+      }
+
+      ///Undo the changes until a snapshot.
+      
+      ///Undo the changes until a snapshot created by save().
+      ///
+      ///\note After you restored a state, you cannot restore
+      ///a later state, in other word you cannot add again the arcs deleted
+      ///by restore().
+      void restore()
+      {
+        _graph->restoreSnapshot(*this);
+      }
+    };
+  };
+  
+} //namespace lemon
+
+
+#endif //LEMON_SMART_GRAPH_H