/* -*- C++ -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library

 *

 * Copyright (C) 2003-2006

 * 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_BITS_GRAPH_EXTENDER_H

#define LEMON_BITS_GRAPH_EXTENDER_H

#include <lemon/bits/invalid.h>

#include <lemon/error.h>

#include <lemon/bits/default_map.h>

///\ingroup graphbits

///\file

///\brief Extenders for the graph types

namespace lemon {

  /// \ingroup graphbits

  ///

  /// \brief Extender for the Graphs

  template <typename Base>

  class GraphExtender : public Base {

  public:

    typedef Base Parent;

    typedef GraphExtender Graph;

    // Base extensions

    typedef typename Parent::Node Node;

    typedef typename Parent::Edge Edge;

    int maxId(Node) const {

      return Parent::maxNodeId();

    }

    int maxId(Edge) const {

      return Parent::maxEdgeId();

    }

    Node fromId(int id, Node) const {

      return Parent::nodeFromId(id);

    }

    Edge fromId(int id, Edge) const {

      return Parent::edgeFromId(id);

    }

    Node oppositeNode(const Node &n, const Edge &e) const {

      if (n == Parent::source(e))

	return Parent::target(e);

      else if(n==Parent::target(e))

	return Parent::source(e);

      else

	return INVALID;

    }

    // Alterable extension

    typedef AlterationNotifier<Node> NodeNotifier;

    typedef AlterationNotifier<Edge> EdgeNotifier;

  protected:

    mutable NodeNotifier node_notifier;

    mutable EdgeNotifier edge_notifier;

  public:

    NodeNotifier& getNotifier(Node) const {

      return node_notifier;

    }

    EdgeNotifier& getNotifier(Edge) const {

      return edge_notifier;

    }

    class NodeIt : public Node { 

      const Graph* graph;

    public:

      NodeIt() {}

      NodeIt(Invalid i) : Node(i) { }

      explicit NodeIt(const Graph& _graph) : graph(&_graph) {

	_graph.first(*static_cast<Node*>(this));

      }

      NodeIt(const Graph& _graph, const Node& node) 

	: Node(node), graph(&_graph) {}

      NodeIt& operator++() { 

	graph->next(*this);

	return *this; 

      }

    };

    class EdgeIt : public Edge { 

      const Graph* graph;

    public:

      EdgeIt() { }

      EdgeIt(Invalid i) : Edge(i) { }

      explicit EdgeIt(const Graph& _graph) : graph(&_graph) {

	_graph.first(*static_cast<Edge*>(this));

      }

      EdgeIt(const Graph& _graph, const Edge& e) : 

	Edge(e), graph(&_graph) { }

      EdgeIt& operator++() { 

	graph->next(*this);

	return *this; 

      }

    };

    class OutEdgeIt : public Edge { 

      const Graph* graph;

    public:

      OutEdgeIt() { }

      OutEdgeIt(Invalid i) : Edge(i) { }

      OutEdgeIt(const Graph& _graph, const Node& node) 

	: graph(&_graph) {

	_graph.firstOut(*this, node);

      }

      OutEdgeIt(const Graph& _graph, const Edge& edge) 

	: Edge(edge), graph(&_graph) {}

      OutEdgeIt& operator++() { 

	graph->nextOut(*this);

	return *this; 

      }

    };

    class InEdgeIt : public Edge { 

      const Graph* graph;

    public:

      InEdgeIt() { }

      InEdgeIt(Invalid i) : Edge(i) { }

      InEdgeIt(const Graph& _graph, const Node& node) 

	: graph(&_graph) {

	_graph.firstIn(*this, node);

      }

      InEdgeIt(const Graph& _graph, const Edge& edge) : 

	Edge(edge), graph(&_graph) {}

      InEdgeIt& operator++() { 

	graph->nextIn(*this);

	return *this; 

      }

    };

    /// \brief Base node of the iterator

    ///

    /// Returns the base node (ie. the source in this case) of the iterator

    Node baseNode(const OutEdgeIt &e) const {

      return Parent::source(e);

    }

    /// \brief Running node of the iterator

    ///

    /// Returns the running node (ie. the target in this case) of the

    /// iterator

    Node runningNode(const OutEdgeIt &e) const {

      return Parent::target(e);

    }

    /// \brief Base node of the iterator

    ///

    /// Returns the base node (ie. the target in this case) of the iterator

    Node baseNode(const InEdgeIt &e) const {

      return Parent::target(e);

    }

    /// \brief Running node of the iterator

    ///

    /// Returns the running node (ie. the source in this case) of the

    /// iterator

    Node runningNode(const InEdgeIt &e) const {

      return Parent::source(e);

    }

    template <typename _Value>

    class NodeMap 

      : public IterableMapExtender<DefaultMap<Graph, Node, _Value> > {

    public:

      typedef GraphExtender Graph;

      typedef IterableMapExtender<DefaultMap<Graph, Node, _Value> > Parent;

      NodeMap(const Graph& _g) 

	: Parent(_g) {}

      NodeMap(const Graph& _g, const _Value& _v) 

	: Parent(_g, _v) {}

      NodeMap& operator=(const NodeMap& cmap) {

	return operator=<NodeMap>(cmap);

      }

      /// \brief Template assign operator.

      ///

      /// The given parameter should be conform to the ReadMap

      /// concecpt and could be indiced by the current item set of

      /// the NodeMap. In this case the value for each item

      /// is assigned by the value of the given ReadMap. 

      template <typename CMap>

      NodeMap& operator=(const CMap& cmap) {

	checkConcept<concept::ReadMap<Node, _Value>, CMap>();

	const typename Parent::Graph* graph = Parent::getGraph();

	Node it;

	for (graph->first(it); it != INVALID; graph->next(it)) {

	  Parent::set(it, cmap[it]);

	}

	return *this;

      }

    };

    template <typename _Value>

    class EdgeMap 

      : public IterableMapExtender<DefaultMap<Graph, Edge, _Value> > {

    public:

      typedef GraphExtender Graph;

      typedef IterableMapExtender<DefaultMap<Graph, Edge, _Value> > Parent;

      EdgeMap(const Graph& _g) 

	: Parent(_g) {}

      EdgeMap(const Graph& _g, const _Value& _v) 

	: Parent(_g, _v) {}

      EdgeMap& operator=(const EdgeMap& cmap) {

	return operator=<EdgeMap>(cmap);

      }

      template <typename CMap>

      EdgeMap& operator=(const CMap& cmap) {

	checkConcept<concept::ReadMap<Edge, _Value>, CMap>();

	const typename Parent::Graph* graph = Parent::getGraph();

	Edge it;

	for (graph->first(it); it != INVALID; graph->next(it)) {

	  Parent::set(it, cmap[it]);

	}

	return *this;

      }

    };

    Node addNode() {

      Node node = Parent::addNode();

      getNotifier(Node()).add(node);

      return node;

    }

    Edge addEdge(const Node& from, const Node& to) {

      Edge edge = Parent::addEdge(from, to);

      getNotifier(Edge()).add(edge);

      return edge;

    }

    void clear() {

      getNotifier(Edge()).clear();

      getNotifier(Node()).clear();

      Parent::clear();

    }

    void erase(const Node& node) {

      Edge edge;

      Parent::firstOut(edge, node);

      while (edge != INVALID ) {

	erase(edge);

	Parent::firstOut(edge, node);

      } 

      Parent::firstIn(edge, node);

      while (edge != INVALID ) {

	erase(edge);

	Parent::firstIn(edge, node);

      }

      getNotifier(Node()).erase(node);

      Parent::erase(node);

    }

    void erase(const Edge& edge) {

      getNotifier(Edge()).erase(edge);

      Parent::erase(edge);

    }

    ~GraphExtender() {

      getNotifier(Edge()).clear();

      getNotifier(Node()).clear();

    }

  };

  /// \ingroup graphbits

  ///

  /// \brief BaseExtender for the UGraphs

  template <typename Base>

  class UGraphBaseExtender : public Base {

  public:

    typedef Base Parent;

    typedef typename Parent::Edge UEdge;

    typedef typename Parent::Node Node;

    typedef True UndirectedTag;

    class Edge : public UEdge {

      friend class UGraphBaseExtender;

    protected:

      bool forward;

      Edge(const UEdge &ue, bool _forward) :

        UEdge(ue), forward(_forward) {}

    public:

      Edge() {}

      /// Invalid edge constructor

      Edge(Invalid i) : UEdge(i), forward(true) {}

      bool operator==(const Edge &that) const {

	return forward==that.forward && UEdge(*this)==UEdge(that);

      }

      bool operator!=(const Edge &that) const {

	return forward!=that.forward || UEdge(*this)!=UEdge(that);

      }

      bool operator<(const Edge &that) const {

	return forward<that.forward ||

	  (!(that.forward<forward) && UEdge(*this)<UEdge(that));

      }

    };

    using Parent::source;

    /// Source of the given Edge.

    Node source(const Edge &e) const {

      return e.forward ? Parent::source(e) : Parent::target(e);

    }

    using Parent::target;

    /// Target of the given Edge.

    Node target(const Edge &e) const {

      return e.forward ? Parent::target(e) : Parent::source(e);

    }

    /// \brief Directed edge from an undirected edge.

    ///

    /// Returns a directed edge corresponding to the specified UEdge.

    /// If the given bool is true the given undirected edge and the

    /// returned edge have the same source node.

    static Edge direct(const UEdge &ue, bool d) {

      return Edge(ue, d);

    }

    /// Returns whether the given directed edge is same orientation as the

    /// corresponding undirected edge.

    ///

    /// \todo reference to the corresponding point of the undirected graph

    /// concept. "What does the direction of an undirected edge mean?"

    static bool direction(const Edge &e) { return e.forward; }

    using Parent::first;

    using Parent::next;

    void first(Edge &e) const {

      Parent::first(e);

      e.forward=true;

    }

    void next(Edge &e) const {

      if( e.forward ) {

	e.forward = false;

      }

      else {

	Parent::next(e);

	e.forward = true;

      }

    }

    void firstOut(Edge &e, const Node &n) const {

      Parent::firstIn(e,n);

      if( UEdge(e) != INVALID ) {

	e.forward = false;

      }

      else {

	Parent::firstOut(e,n);

	e.forward = true;

      }

    }

    void nextOut(Edge &e) const {

      if( ! e.forward ) {

	Node n = Parent::target(e);

	Parent::nextIn(e);

	if( UEdge(e) == INVALID ) {

	  Parent::firstOut(e, n);

	  e.forward = true;

	}

      }

      else {

	Parent::nextOut(e);

      }

    }

    void firstIn(Edge &e, const Node &n) const {

      Parent::firstOut(e,n);

      if( UEdge(e) != INVALID ) {

	e.forward = false;

      }

      else {

	Parent::firstIn(e,n);

	e.forward = true;

      }

    }

    void nextIn(Edge &e) const {

      if( ! e.forward ) {

	Node n = Parent::source(e);

	Parent::nextOut(e);

	if( UEdge(e) == INVALID ) {

	  Parent::firstIn(e, n);

	  e.forward = true;

	}

      }

      else {

	Parent::nextIn(e);

      }

    }

    void firstInc(UEdge &e, bool &d, const Node &n) const {

      d = true;

      Parent::firstOut(e, n);

      if (e != INVALID) return;

      d = false;

      Parent::firstIn(e, n);

    }

    void nextInc(UEdge &e, bool &d) const {

      if (d) {

	Node s = Parent::source(e);

	Parent::nextOut(e);

	if (e != INVALID) return;

	d = false;

	Parent::firstIn(e, s);

      } else {

	Parent::nextIn(e);

      }

    }

    Node nodeFromId(int id) const {

      return Parent::nodeFromId(id);

    }

    Edge edgeFromId(int id) const {

      return direct(Parent::edgeFromId(id >> 1), bool(id & 1));

    }

    UEdge uEdgeFromId(int id) const {

      return Parent::edgeFromId(id >> 1);

    }

    int id(const Node &n) const {

      return Parent::id(n);

    }

    int id(const UEdge &e) const {

      return Parent::id(e);

    }

    int id(const Edge &e) const {

      return 2 * Parent::id(e) + int(e.forward);

    }

    int maxNodeId() const {

      return Parent::maxNodeId();

    }

    int maxEdgeId() const {

      return 2 * Parent::maxEdgeId() + 1;

    }

    int maxUEdgeId() const {

      return Parent::maxEdgeId();

    }

    int edgeNum() const {

      return 2 * Parent::edgeNum();

    }

    int uEdgeNum() const {

      return Parent::edgeNum();

    }

    Edge findEdge(Node source, Node target, Edge prev) const {

      if (prev == INVALID) {

	UEdge edge = Parent::findEdge(source, target);

	if (edge != INVALID) return direct(edge, true);

	edge = Parent::findEdge(target, source);

	if (edge != INVALID) return direct(edge, false);

      } else if (direction(prev)) {

	UEdge edge = Parent::findEdge(source, target, prev);

	if (edge != INVALID) return direct(edge, true);

	edge = Parent::findEdge(target, source);

	if (edge != INVALID) return direct(edge, false);	

      } else {

	UEdge edge = Parent::findEdge(target, source, prev);

	if (edge != INVALID) return direct(edge, false);	      

      }

      return INVALID;

    }

    UEdge findUEdge(Node source, Node target, UEdge prev) const {

      if (prev == INVALID) {

	UEdge edge = Parent::findEdge(source, target);

	if (edge != INVALID) return edge;

	edge = Parent::findEdge(target, source);

	if (edge != INVALID) return edge;

      } else if (Parent::source(prev) == source) {

	UEdge edge = Parent::findEdge(source, target, prev);

	if (edge != INVALID) return edge;

	edge = Parent::findEdge(target, source);

	if (edge != INVALID) return edge;	

      } else {

	UEdge edge = Parent::findEdge(target, source, prev);

	if (edge != INVALID) return edge;	      

      }

      return INVALID;

    }

  };

  /// \ingroup graphbits

  ///

  /// \brief Extender for the UGraphs

  template <typename Base> 

  class UGraphExtender : public Base {

  public:

    typedef Base Parent;

    typedef UGraphExtender Graph;

    typedef typename Parent::Node Node;

    typedef typename Parent::Edge Edge;

    typedef typename Parent::UEdge UEdge;

    // UGraph extension    

    int maxId(Node) const {

      return Parent::maxNodeId();

    }

    int maxId(Edge) const {

      return Parent::maxEdgeId();

    }

    int maxId(UEdge) const {

      return Parent::maxUEdgeId();

    }

    Node fromId(int id, Node) const {

      return Parent::nodeFromId(id);

    }

    Edge fromId(int id, Edge) const {

      return Parent::edgeFromId(id);

    }

    UEdge fromId(int id, UEdge) const {

      return Parent::uEdgeFromId(id);

    }

    Node oppositeNode(const Node &n, const UEdge &e) const {

      if( n == Parent::source(e))

	return Parent::target(e);

      else if( n == Parent::target(e))

	return Parent::source(e);

      else

	return INVALID;

    }

    Edge oppositeEdge(const Edge &e) const {

      return Parent::direct(e, !Parent::direction(e));

    }

    using Parent::direct;

    Edge direct(const UEdge &ue, const Node &s) const {

      return Parent::direct(ue, Parent::source(ue) == s);

    }

    // Alterable extension

    typedef AlterationNotifier<Node> NodeNotifier;

    typedef AlterationNotifier<Edge> EdgeNotifier;

    typedef AlterationNotifier<UEdge> UEdgeNotifier;

  protected:

    mutable NodeNotifier node_notifier;

    mutable EdgeNotifier edge_notifier;

    mutable UEdgeNotifier uedge_notifier;

  public:

    NodeNotifier& getNotifier(Node) const {

      return node_notifier;

    }

    EdgeNotifier& getNotifier(Edge) const {

      return edge_notifier;

    }

    UEdgeNotifier& getNotifier(UEdge) const {

      return uedge_notifier;

    }

    class NodeIt : public Node { 

      const Graph* graph;

    public:

      NodeIt() {}

      NodeIt(Invalid i) : Node(i) { }

      explicit NodeIt(const Graph& _graph) : graph(&_graph) {

	_graph.first(*static_cast<Node*>(this));

      }

      NodeIt(const Graph& _graph, const Node& node) 

	: Node(node), graph(&_graph) {}

      NodeIt& operator++() { 

	graph->next(*this);

	return *this; 

      }

    };

    class EdgeIt : public Edge { 

      const Graph* graph;

    public:

      EdgeIt() { }

      EdgeIt(Invalid i) : Edge(i) { }

      explicit EdgeIt(const Graph& _graph) : graph(&_graph) {

	_graph.first(*static_cast<Edge*>(this));

      }

      EdgeIt(const Graph& _graph, const Edge& e) : 

	Edge(e), graph(&_graph) { }

      EdgeIt& operator++() { 

	graph->next(*this);

	return *this; 

      }

    };

    class OutEdgeIt : public Edge { 

      const Graph* graph;

    public:

      OutEdgeIt() { }

      OutEdgeIt(Invalid i) : Edge(i) { }

      OutEdgeIt(const Graph& _graph, const Node& node) 

	: graph(&_graph) {

	_graph.firstOut(*this, node);

      }

      OutEdgeIt(const Graph& _graph, const Edge& edge) 

	: Edge(edge), graph(&_graph) {}

      OutEdgeIt& operator++() { 

	graph->nextOut(*this);

	return *this; 

      }

    };

    class InEdgeIt : public Edge { 

      const Graph* graph;

    public:

      InEdgeIt() { }

      InEdgeIt(Invalid i) : Edge(i) { }

      InEdgeIt(const Graph& _graph, const Node& node) 

	: graph(&_graph) {

	_graph.firstIn(*this, node);

      }

      InEdgeIt(const Graph& _graph, const Edge& edge) : 

	Edge(edge), graph(&_graph) {}

      InEdgeIt& operator++() { 

	graph->nextIn(*this);

	return *this; 

      }

    };

    class UEdgeIt : public Parent::UEdge { 

      const Graph* graph;

    public:

      UEdgeIt() { }

      UEdgeIt(Invalid i) : UEdge(i) { }

      explicit UEdgeIt(const Graph& _graph) : graph(&_graph) {

	_graph.first(*static_cast<UEdge*>(this));

      }

      UEdgeIt(const Graph& _graph, const UEdge& e) : 

	UEdge(e), graph(&_graph) { }

      UEdgeIt& operator++() { 

	graph->next(*this);

	return *this; 

      }

    };

    class IncEdgeIt : public Parent::UEdge {

      friend class UGraphExtender;

      const Graph* graph;

      bool direction;

    public:

      IncEdgeIt() { }

      IncEdgeIt(Invalid i) : UEdge(i), direction(false) { }

      IncEdgeIt(const Graph& _graph, const Node &n) : graph(&_graph) {

	_graph.firstInc(*this, direction, n);

      }

      IncEdgeIt(const Graph& _graph, const UEdge &ue, const Node &n)

	: graph(&_graph), UEdge(ue) {

	direction = (_graph.source(ue) == n);

      }

      IncEdgeIt& operator++() {

	graph->nextInc(*this, direction);

	return *this; 

      }

    };

    /// \brief Base node of the iterator

    ///

    /// Returns the base node (ie. the source in this case) of the iterator

    Node baseNode(const OutEdgeIt &e) const {

      return Parent::source((Edge)e);

    }

    /// \brief Running node of the iterator

    ///

    /// Returns the running node (ie. the target in this case) of the

    /// iterator

    Node runningNode(const OutEdgeIt &e) const {

      return Parent::target((Edge)e);

    }

    /// \brief Base node of the iterator

    ///

    /// Returns the base node (ie. the target in this case) of the iterator

    Node baseNode(const InEdgeIt &e) const {

      return Parent::target((Edge)e);

    }

    /// \brief Running node of the iterator

    ///

    /// Returns the running node (ie. the source in this case) of the

    /// iterator

    Node runningNode(const InEdgeIt &e) const {

      return Parent::source((Edge)e);

    }

    /// Base node of the iterator

    ///

    /// Returns the base node of the iterator

    Node baseNode(const IncEdgeIt &e) const {

      return e.direction ? source(e) : target(e);

    }

    /// Running node of the iterator

    ///

    /// Returns the running node of the iterator

    Node runningNode(const IncEdgeIt &e) const {

      return e.direction ? target(e) : source(e);

    }

    // Mappable extension

    template <typename _Value>

    class NodeMap 

      : public IterableMapExtender<DefaultMap<Graph, Node, _Value> > {

    public:

      typedef UGraphExtender Graph;

      typedef IterableMapExtender<DefaultMap<Graph, Node, _Value> > Parent;

      NodeMap(const Graph& _g) 

	: Parent(_g) {}

      NodeMap(const Graph& _g, const _Value& _v) 

	: Parent(_g, _v) {}

      NodeMap& operator=(const NodeMap& cmap) {

	return operator=<NodeMap>(cmap);

      }

      /// \brief Template assign operator.

      ///

      /// The given parameter should be conform to the ReadMap

      /// concecpt and could be indiced by the current item set of

      /// the NodeMap. In this case the value for each item

      /// is assigned by the value of the given ReadMap. 

      template <typename CMap>

      NodeMap& operator=(const CMap& cmap) {

	checkConcept<concept::ReadMap<Node, _Value>, CMap>();

	const typename Parent::Graph* graph = Parent::getGraph();

	Node it;

	for (graph->first(it); it != INVALID; graph->next(it)) {

	  Parent::set(it, cmap[it]);

	}

	return *this;

      }

    };

    template <typename _Value>

    class EdgeMap 

      : public IterableMapExtender<DefaultMap<Graph, Edge, _Value> > {

    public:

      typedef UGraphExtender Graph;

      typedef IterableMapExtender<DefaultMap<Graph, Edge, _Value> > Parent;

      EdgeMap(const Graph& _g) 

	: Parent(_g) {}

      EdgeMap(const Graph& _g, const _Value& _v) 

	: Parent(_g, _v) {}

      EdgeMap& operator=(const EdgeMap& cmap) {

	return operator=<EdgeMap>(cmap);

      }

      template <typename CMap>

      EdgeMap& operator=(const CMap& cmap) {

	checkConcept<concept::ReadMap<Edge, _Value>, CMap>();

	const typename Parent::Graph* graph = Parent::getGraph();

	Edge it;

	for (graph->first(it); it != INVALID; graph->next(it)) {

	  Parent::set(it, cmap[it]);

	}

	return *this;

      }

    };

    template <typename _Value>

    class UEdgeMap 

      : public IterableMapExtender<DefaultMap<Graph, UEdge, _Value> > {

    public:

      typedef UGraphExtender Graph;

      typedef IterableMapExtender<DefaultMap<Graph, UEdge, _Value> > Parent;

      UEdgeMap(const Graph& _g) 

	: Parent(_g) {}

      UEdgeMap(const Graph& _g, const _Value& _v) 

	: Parent(_g, _v) {}

      UEdgeMap& operator=(const UEdgeMap& cmap) {

	return operator=<UEdgeMap>(cmap);

      }

      template <typename CMap>

      UEdgeMap& operator=(const CMap& cmap) {

	checkConcept<concept::ReadMap<UEdge, _Value>, CMap>();

	const typename Parent::Graph* graph = Parent::getGraph();

	UEdge it;

	for (graph->first(it); it != INVALID; graph->next(it)) {

	  Parent::set(it, cmap[it]);

	}

	return *this;

      }

    };

    // Alteration extension

    Node addNode() {

      Node node = Parent::addNode();

      getNotifier(Node()).add(node);

      return node;

    }

    UEdge addEdge(const Node& from, const Node& to) {

      UEdge uedge = Parent::addEdge(from, to);

      getNotifier(UEdge()).add(uedge);

      getNotifier(Edge()).add(Parent::direct(uedge, true));

      getNotifier(Edge()).add(Parent::direct(uedge, false));

      return uedge;

    }

    void clear() {

      getNotifier(Edge()).clear();

      getNotifier(UEdge()).clear();

      getNotifier(Node()).clear();

      Parent::clear();

    }

    void erase(const Node& node) {

      Edge edge;

      Parent::firstOut(edge, node);

      while (edge != INVALID ) {

	erase(edge);

	Parent::firstOut(edge, node);

      } 

      Parent::firstIn(edge, node);

      while (edge != INVALID ) {

	erase(edge);

	Parent::firstIn(edge, node);

      }

      getNotifier(Node()).erase(node);

      Parent::erase(node);

    }

    void erase(const UEdge& uedge) {

      getNotifier(Edge()).erase(Parent::direct(uedge, true));

      getNotifier(Edge()).erase(Parent::direct(uedge, false));

      getNotifier(UEdge()).erase(uedge);

      Parent::erase(uedge);

    }

    ~UGraphExtender() {

      getNotifier(Edge()).clear();

      getNotifier(UEdge()).clear();

      getNotifier(Node()).clear();

    }

  };

  /// \ingroup graphbits