diff --git a/lemon/fourary_heap.h b/lemon/fourary_heap.h
new file mode 100644
--- /dev/null
+++ b/lemon/fourary_heap.h
@@ -0,0 +1,342 @@
+/* -*- mode: C++; indent-tabs-mode: nil; -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library.
+ *
+ * Copyright (C) 2003-2009
+ * 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_FOURARY_HEAP_H
+#define LEMON_FOURARY_HEAP_H
+
+///\ingroup heaps
+///\file
+///\brief Fourary heap implementation.
+
+#include <vector>
+#include <utility>
+#include <functional>
+
+namespace lemon {
+
+  /// \ingroup heaps
+  ///
+  ///\brief Fourary heap data structure.
+  ///
+  /// This class implements the \e fourary \e heap data structure.
+  /// It fully conforms to the \ref concepts::Heap "heap concept".
+  ///
+  /// The fourary heap is a specialization of the \ref KaryHeap "K-ary heap"
+  /// for <tt>K=4</tt>. It is similar to the \ref BinHeap "binary heap",
+  /// but its nodes have at most four children, instead of two.
+  ///
+  /// \tparam PR Type of the priorities of the items.
+  /// \tparam IM A read-writable item map with \c int values, used
+  /// internally to handle the cross references.
+  /// \tparam CMP A functor class for comparing the priorities.
+  /// The default is \c std::less<PR>.
+  ///
+  ///\sa BinHeap
+  ///\sa KaryHeap
+#ifdef DOXYGEN
+  template <typename PR, typename IM, typename CMP>
+#else
+  template <typename PR, typename IM, typename CMP = std::less<PR> >
+#endif
+  class FouraryHeap {
+  public:
+    /// Type of the item-int map.
+    typedef IM ItemIntMap;
+    /// Type of the priorities.
+    typedef PR Prio;
+    /// Type of the items stored in the heap.
+    typedef typename ItemIntMap::Key Item;
+    /// Type of the item-priority pairs.
+    typedef std::pair<Item,Prio> Pair;
+    /// Functor type for comparing the priorities.
+    typedef CMP Compare;
+
+    /// \brief Type to represent the states of the items.
+    ///
+    /// Each item has a state associated to it. It can be "in heap",
+    /// "pre-heap" or "post-heap". The latter two are indifferent from the
+    /// heap's point of view, but may be useful to the user.
+    ///
+    /// The item-int map must be initialized in such way that it assigns
+    /// \c PRE_HEAP (<tt>-1</tt>) to any element to be put in the heap.
+    enum State {
+      IN_HEAP = 0,    ///< = 0.
+      PRE_HEAP = -1,  ///< = -1.
+      POST_HEAP = -2  ///< = -2.
+    };
+
+  private:
+    std::vector<Pair> _data;
+    Compare _comp;
+    ItemIntMap &_iim;
+
+  public:
+    /// \brief Constructor.
+    ///
+    /// Constructor.
+    /// \param map A map that assigns \c int values to the items.
+    /// It is used internally to handle the cross references.
+    /// The assigned value must be \c PRE_HEAP (<tt>-1</tt>) for each item.
+    explicit FouraryHeap(ItemIntMap &map) : _iim(map) {}
+
+    /// \brief Constructor.
+    ///
+    /// Constructor.
+    /// \param map A map that assigns \c int values to the items.
+    /// It is used internally to handle the cross references.
+    /// The assigned value must be \c PRE_HEAP (<tt>-1</tt>) for each item.
+    /// \param comp The function object used for comparing the priorities.
+    FouraryHeap(ItemIntMap &map, const Compare &comp)
+      : _iim(map), _comp(comp) {}
+
+    /// \brief The number of items stored in the heap.
+    ///
+    /// This function returns the number of items stored in the heap.
+    int size() const { return _data.size(); }
+
+    /// \brief Check if the heap is empty.
+    ///
+    /// This function returns \c true if the heap is empty.
+    bool empty() const { return _data.empty(); }
+
+    /// \brief Make the heap empty.
+    ///
+    /// This functon makes the heap empty.
+    /// It does not change the cross reference map. If you want to reuse
+    /// a heap that is not surely empty, you should first clear it and
+    /// then you should set the cross reference map to \c PRE_HEAP
+    /// for each item.
+    void clear() { _data.clear(); }
+
+  private:
+    static int parent(int i) { return (i-1)/4; }
+    static int firstChild(int i) { return 4*i+1; }
+
+    bool less(const Pair &p1, const Pair &p2) const {
+      return _comp(p1.second, p2.second);
+    }
+
+    void bubbleUp(int hole, Pair p) {
+      int par = parent(hole);
+      while( hole>0 && less(p,_data[par]) ) {
+        move(_data[par],hole);
+        hole = par;
+        par = parent(hole);
+      }
+      move(p, hole);
+    }
+
+    void bubbleDown(int hole, Pair p, int length) {
+      if( length>1 ) {
+        int child = firstChild(hole);
+        while( child+3<length ) {
+          int min=child;
+          if( less(_data[++child], _data[min]) ) min=child;
+          if( less(_data[++child], _data[min]) ) min=child;
+          if( less(_data[++child], _data[min]) ) min=child;
+          if( !less(_data[min], p) )
+            goto ok;
+          move(_data[min], hole);
+          hole = min;
+          child = firstChild(hole);
+        }
+        if ( child<length ) {
+          int min = child;
+          if( ++child<length && less(_data[child], _data[min]) ) min=child;
+          if( ++child<length && less(_data[child], _data[min]) ) min=child;
+          if( less(_data[min], p) ) {
+            move(_data[min], hole);
+            hole = min;
+          }
+        }
+      }
+    ok:
+      move(p, hole);
+    }
+
+    void move(const Pair &p, int i) {
+      _data[i] = p;
+      _iim.set(p.first, i);
+    }
+
+  public:
+    /// \brief Insert a pair of item and priority into the heap.
+    ///
+    /// This function inserts \c p.first to the heap with priority
+    /// \c p.second.
+    /// \param p The pair to insert.
+    /// \pre \c p.first must not be stored in the heap.
+    void push(const Pair &p) {
+      int n = _data.size();
+      _data.resize(n+1);
+      bubbleUp(n, p);
+    }
+
+    /// \brief Insert an item into the heap with the given priority.
+    ///
+    /// This function inserts the given item into the heap with the
+    /// given priority.
+    /// \param i The item to insert.
+    /// \param p The priority of the item.
+    /// \pre \e i must not be stored in the heap.
+    void push(const Item &i, const Prio &p) { push(Pair(i,p)); }
+
+    /// \brief Return the item having minimum priority.
+    ///
+    /// This function returns the item having minimum priority.
+    /// \pre The heap must be non-empty.
+    Item top() const { return _data[0].first; }
+
+    /// \brief The minimum priority.
+    ///
+    /// This function returns the minimum priority.
+    /// \pre The heap must be non-empty.
+    Prio prio() const { return _data[0].second; }
+
+    /// \brief Remove the item having minimum priority.
+    ///
+    /// This function removes the item having minimum priority.
+    /// \pre The heap must be non-empty.
+    void pop() {
+      int n = _data.size()-1;
+      _iim.set(_data[0].first, POST_HEAP);
+      if (n>0) bubbleDown(0, _data[n], n);
+      _data.pop_back();
+    }
+
+    /// \brief Remove the given item from the heap.
+    ///
+    /// This function removes the given item from the heap if it is
+    /// already stored.
+    /// \param i The item to delete.
+    /// \pre \e i must be in the heap.
+    void erase(const Item &i) {
+      int h = _iim[i];
+      int n = _data.size()-1;
+      _iim.set(_data[h].first, POST_HEAP);
+      if( h<n ) {
+        if( less(_data[parent(h)], _data[n]) )
+          bubbleDown(h, _data[n], n);
+        else
+          bubbleUp(h, _data[n]);
+      }
+      _data.pop_back();
+    }
+
+    /// \brief The priority of the given item.
+    ///
+    /// This function returns the priority of the given item.
+    /// \param i The item.
+    /// \pre \e i must be in the heap.
+    Prio operator[](const Item &i) const {
+      int idx = _iim[i];
+      return _data[idx].second;
+    }
+
+    /// \brief Set the priority of an item or insert it, if it is
+    /// not stored in the heap.
+    ///
+    /// This method sets the priority of the given item if it is
+    /// already stored in the heap. Otherwise it inserts the given
+    /// item into the heap with the given priority.
+    /// \param i The item.
+    /// \param p The priority.
+    void set(const Item &i, const Prio &p) {
+      int idx = _iim[i];
+      if( idx < 0 )
+        push(i,p);
+      else if( _comp(p, _data[idx].second) )
+        bubbleUp(idx, Pair(i,p));
+      else
+        bubbleDown(idx, Pair(i,p), _data.size());
+    }
+
+    /// \brief Decrease the priority of an item to the given value.
+    ///
+    /// This function decreases the priority of an item to the given value.
+    /// \param i The item.
+    /// \param p The priority.
+    /// \pre \e i must be stored in the heap with priority at least \e p.
+    void decrease(const Item &i, const Prio &p) {
+      int idx = _iim[i];
+      bubbleUp(idx, Pair(i,p));
+    }
+
+    /// \brief Increase the priority of an item to the given value.
+    ///
+    /// This function increases the priority of an item to the given value.
+    /// \param i The item.
+    /// \param p The priority.
+    /// \pre \e i must be stored in the heap with priority at most \e p.
+    void increase(const Item &i, const Prio &p) {
+      int idx = _iim[i];
+      bubbleDown(idx, Pair(i,p), _data.size());
+    }
+
+    /// \brief Return the state of an item.
+    ///
+    /// This method returns \c PRE_HEAP if the given item has never
+    /// been in the heap, \c IN_HEAP if it is in the heap at the moment,
+    /// and \c POST_HEAP otherwise.
+    /// In the latter case it is possible that the item will get back
+    /// to the heap again.
+    /// \param i The item.
+    State state(const Item &i) const {
+      int s = _iim[i];
+      if (s>=0) s=0;
+      return State(s);
+    }
+
+    /// \brief Set the state of an item in the heap.
+    ///
+    /// This function sets the state of the given item in the heap.
+    /// It can be used to manually clear the heap when it is important
+    /// to achive better time complexity.
+    /// \param i The item.
+    /// \param st The state. It should not be \c IN_HEAP.
+    void state(const Item& i, State st) {
+      switch (st) {
+        case POST_HEAP:
+        case PRE_HEAP:
+          if (state(i) == IN_HEAP) erase(i);
+          _iim[i] = st;
+          break;
+        case IN_HEAP:
+          break;
+      }
+    }
+
+    /// \brief Replace an item in the heap.
+    ///
+    /// This function replaces item \c i with item \c j.
+    /// Item \c i must be in the heap, while \c j must be out of the heap.
+    /// After calling this method, item \c i will be out of the
+    /// heap and \c j will be in the heap with the same prioriority
+    /// as item \c i had before.
+    void replace(const Item& i, const Item& j) {
+      int idx = _iim[i];
+      _iim.set(i, _iim[j]);
+      _iim.set(j, idx);
+      _data[idx].first = j;
+    }
+
+  }; // class FouraryHeap
+
+} // namespace lemon
+
+#endif // LEMON_FOURARY_HEAP_H