/*

   $Id: tree.hh,v 1.147 2007/10/19 11:24:24 peekas Exp $

   STL-like templated tree class.
   SPDX-FileCopyrightText: 2001-2006  Kasper Peeters <kasper.peeters@aei.mpg.de>.
   SPDX-License-Identifier: GPL-2.0-only or GPL-3.0-only
*/

/** \mainpage tree.hh
    \author   Kasper Peeters
    \version  2.4
    \date     18-Oct-2007
    \see      http://www.aei.mpg.de/~peekas/tree/
    \see      http://www.aei.mpg.de/~peekas/tree/ChangeLog

   The tree.hh library for C++ provides an STL-like container class
   for n-ary trees, templated over the data stored at the
   nodes. Various types of iterators are provided (post-order,
   pre-order, and others). Where possible the access methods are
   compatible with the STL or alternative algorithms are
   available.
*/

/*
   The tree.hh code is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 or 3.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor,
   Boston, MA  02110-1301  USA
*/

/** \todo
   - New-style move members are not completely finished yet.
   - It would be good to have an iterator which can iterate over all
     nodes below a given node.
   - Fixed depth iterators do not iterate over the entire range if there
     are 'holes' in the tree.
   - If a range uses const iter_base& as end iterator, things will
     inevitably go wrong, because upcast from iter_base to a non-sibling_iter
     is incorrect. This upcast should be removed (and then all illegal uses
     as previously in 'equal' will be flagged by the compiler). This requires
     new copy constructors though.
   - There's a bug in replace(sibling_iterator, ...) when the ranges
     sit next to each other. Turned up in append_child(iter,iter)
     but has been avoided now.
   - "std::operator<" does not work correctly on our iterators, and for some
     reason a globally defined template operator< did not get picked up.
     Using a comparison class now, but this should be investigated.
*/

#ifndef tree_hh_
#    define tree_hh_

#    include <cassert>
#    include <memory>
#    include <stdexcept>
#    include <iterator>
#    include <set>
#    include <queue>
#    include <iostream>

// HP-style construct/destroy have gone from the standard,
// so here is a copy.

namespace kp {

template<class T1, class T2>
void constructor(T1 *p, T2 &val)
{
    new ((void *)p) T1(val);
}

template<class T1>
void constructor(T1 *p)
{
    new ((void *)p) T1;
}

template<class T1>
void destructor(T1 *p)
{
    p->~T1();
}

}

/// A node in the tree, combining links to other nodes as well as the actual data.
template<class T>
class tree_node_
{ // size: 5*4=20 bytes (on 32 bit arch), can be reduced by 8.
public:
    tree_node_<T> *parent;
    tree_node_<T> *first_child, *last_child;
    tree_node_<T> *prev_sibling, *next_sibling;
    T data;
}; // __attribute__((packed));

template<class T, class tree_node_allocator = std::allocator<tree_node_<T>>>
class tree
{
protected:
    typedef tree_node_<T> tree_node;

public:
    /// Value of the data stored at a node.
    typedef T value_type;

    class iterator_base;
    class pre_order_iterator;
    class post_order_iterator;
    class sibling_iterator;
    class leaf_iterator;

    tree();
    tree(const T &);
    tree(const iterator_base &);
    tree(const tree<T, tree_node_allocator> &);
    ~tree();
    void operator=(const tree<T, tree_node_allocator> &);

    /// Base class for iterators, only pointers stored, no traversal logic.
#    ifdef __SGI_STL_PORT
    class iterator_base : public stlport::bidirectional_iterator<T, ptrdiff_t>
    {
#    else
    class iterator_base
    {
#    endif
    public:
        typedef T value_type;
        typedef T *pointer;
        typedef T &reference;
        typedef size_t size_type;
        typedef ptrdiff_t difference_type;
        typedef std::bidirectional_iterator_tag iterator_category;

        iterator_base();
        iterator_base(tree_node *);

        T &operator*() const;
        T *operator->() const;

        /// When called, the next increment/decrement skips children of this node.
        void skip_children();
        /// Number of children of the node pointed to by the iterator.
        unsigned int number_of_children() const;

        sibling_iterator begin() const;
        sibling_iterator end() const;

        tree_node *node;

    protected:
        bool skip_current_children_;
    };

    /// Depth-first iterator, first accessing the node, then its children.
    class pre_order_iterator : public iterator_base
    {
    public:
        pre_order_iterator();
        pre_order_iterator(tree_node *);
        pre_order_iterator(const iterator_base &);
        pre_order_iterator(const sibling_iterator &);

        bool operator==(const pre_order_iterator &) const;
        bool operator!=(const pre_order_iterator &) const;
        pre_order_iterator &operator++();
        pre_order_iterator &operator--();
        pre_order_iterator operator++(int);
        pre_order_iterator operator--(int);
        pre_order_iterator &operator+=(unsigned int);
        pre_order_iterator &operator-=(unsigned int);
    };

    /// Depth-first iterator, first accessing the children, then the node itself.
    class post_order_iterator : public iterator_base
    {
    public:
        post_order_iterator();
        post_order_iterator(tree_node *);
        post_order_iterator(const iterator_base &);
        post_order_iterator(const sibling_iterator &);

        bool operator==(const post_order_iterator &) const;
        bool operator!=(const post_order_iterator &) const;
        post_order_iterator &operator++();
        post_order_iterator &operator--();
        post_order_iterator operator++(int);
        post_order_iterator operator--(int);
        post_order_iterator &operator+=(unsigned int);
        post_order_iterator &operator-=(unsigned int);

        /// Set iterator to the first child as deep as possible down the tree.
        void descend_all();
    };

    /// Breadth-first iterator, using a queue
    class breadth_first_queued_iterator : public iterator_base
    {
    public:
        breadth_first_queued_iterator();
        breadth_first_queued_iterator(tree_node *);
        breadth_first_queued_iterator(const iterator_base &);

        bool operator==(const breadth_first_queued_iterator &) const;
        bool operator!=(const breadth_first_queued_iterator &) const;
        breadth_first_queued_iterator &operator++();
        breadth_first_queued_iterator operator++(int);
        breadth_first_queued_iterator &operator+=(unsigned int);

    private:
        std::queue<tree_node *> traversal_queue;
    };

    /// The default iterator types throughout the tree class.
    typedef pre_order_iterator iterator;
    typedef breadth_first_queued_iterator breadth_first_iterator;

    /// Iterator which traverses only the nodes at a given depth from the root.
    class fixed_depth_iterator : public iterator_base
    {
    public:
        fixed_depth_iterator();
        fixed_depth_iterator(tree_node *);
        fixed_depth_iterator(const iterator_base &);
        fixed_depth_iterator(const sibling_iterator &);
        fixed_depth_iterator(const fixed_depth_iterator &);

        bool operator==(const fixed_depth_iterator &) const;
        bool operator!=(const fixed_depth_iterator &) const;
        fixed_depth_iterator &operator++();
        fixed_depth_iterator &operator--();
        fixed_depth_iterator operator++(int);
        fixed_depth_iterator operator--(int);
        fixed_depth_iterator &operator+=(unsigned int);
        fixed_depth_iterator &operator-=(unsigned int);

        tree_node *first_parent_;

    private:
        void set_first_parent_();
        void find_leftmost_parent_();
    };

    /// Iterator which traverses only the nodes which are siblings of each other.
    class sibling_iterator : public iterator_base
    {
    public:
        sibling_iterator();
        sibling_iterator(tree_node *);
        sibling_iterator(const sibling_iterator &);
        sibling_iterator(const iterator_base &);

        bool operator==(const sibling_iterator &) const;
        bool operator!=(const sibling_iterator &) const;
        sibling_iterator &operator++();
        sibling_iterator &operator--();
        sibling_iterator operator++(int);
        sibling_iterator operator--(int);
        sibling_iterator &operator+=(unsigned int);
        sibling_iterator &operator-=(unsigned int);

        tree_node *range_first() const;
        tree_node *range_last() const;
        tree_node *parent_;

    private:
        void set_parent_();
    };

    /// Iterator which traverses only the leaves.
    class leaf_iterator : public iterator_base
    {
    public:
        leaf_iterator();
        leaf_iterator(tree_node *);
        leaf_iterator(const sibling_iterator &);
        leaf_iterator(const iterator_base &);

        bool operator==(const leaf_iterator &) const;
        bool operator!=(const leaf_iterator &) const;
        leaf_iterator &operator++();
        leaf_iterator &operator--();
        leaf_iterator operator++(int);
        leaf_iterator operator--(int);
        leaf_iterator &operator+=(unsigned int);
        leaf_iterator &operator-=(unsigned int);
    };

    /// Return iterator to the beginning of the tree.
    inline pre_order_iterator begin() const;
    /// Return iterator to the end of the tree.
    inline pre_order_iterator end() const;
    /// Return post-order iterator to the beginning of the tree.
    post_order_iterator begin_post() const;
    /// Return post-order iterator to the end of the tree.
    post_order_iterator end_post() const;
    /// Return fixed-depth iterator to the first node at a given depth from the given iterator.
    fixed_depth_iterator begin_fixed(const iterator_base &, unsigned int) const;
    /// Return fixed-depth iterator to end of the nodes at given depth from the given iterator.
    fixed_depth_iterator end_fixed(const iterator_base &, unsigned int) const;
    /// Return breadth-first iterator to the first node at a given depth.
    breadth_first_queued_iterator begin_breadth_first() const;
    /// Return breadth-first iterator to end of the nodes at given depth.
    breadth_first_queued_iterator end_breadth_first() const;
    /// Return sibling iterator to the first child of given node.
    sibling_iterator begin(const iterator_base &) const;
    /// Return sibling iterator to the end of the children of a given node.
    sibling_iterator end(const iterator_base &) const;
    /// Return leaf iterator to the first leaf of the tree.
    leaf_iterator begin_leaf() const;
    /// Return leaf iterator to the last leaf of the tree.
    leaf_iterator end_leaf() const;

    /// Return iterator to the parent of a node.
    template<typename iter>
    static iter parent(iter);
    /// Return iterator to the previous sibling of a node.
    template<typename iter>
    iter previous_sibling(iter) const;
    /// Return iterator to the next sibling of a node.
    template<typename iter>
    iter next_sibling(iter) const;
    /// Return iterator to the next node at a given depth.
    template<typename iter>
    iter next_at_same_depth(iter) const;

    /// Erase all nodes of the tree.
    void clear();
    /// Erase element at position pointed to by iterator, return incremented iterator.
    template<typename iter>
    iter erase(iter);
    /// Erase all children of the node pointed to by iterator.
    void erase_children(const iterator_base &);

    /// Insert empty node as last/first child of node pointed to by position.
    template<typename iter>
    iter append_child(iter position);
    template<typename iter>
    iter prepend_child(iter position);
    /// Insert node as last/first child of node pointed to by position.
    template<typename iter>
    iter append_child(iter position, const T &x);
    template<typename iter>
    iter prepend_child(iter position, const T &x);
    /// Append the node (plus its children) at other_position as last/first child of position.
    template<typename iter>
    iter append_child(iter position, iter other_position);
    template<typename iter>
    iter prepend_child(iter position, iter other_position);
    /// Append the nodes in the from-to range (plus their children) as last/first children of
    /// position.
    template<typename iter>
    iter append_children(iter position, sibling_iterator from, sibling_iterator to);
    template<typename iter>
    iter prepend_children(iter position, sibling_iterator from, sibling_iterator to);

    /// Short-hand to insert topmost node in otherwise empty tree.
    pre_order_iterator set_head(const T &x);
    /// Insert node as previous sibling of node pointed to by position.
    template<typename iter>
    iter insert(iter position, const T &x);
    /// Specialisation of previous member.
    sibling_iterator insert(sibling_iterator position, const T &x);
    /// Insert node (with children) pointed to by subtree as previous sibling of node pointed to by
    /// position.
    template<typename iter>
    iter insert_subtree(iter position, const iterator_base &subtree);
    /// Insert node as next sibling of node pointed to by position.
    template<typename iter>
    iter insert_after(iter position, const T &x);
    /// Insert node (with children) pointed to by subtree as next sibling of node pointed to by
    /// position.
    template<typename iter>
    iter insert_subtree_after(iter position, const iterator_base &subtree);

    /// Replace node at 'position' with other node (keeping same children); 'position' becomes
    /// invalid.
    template<typename iter>
    iter replace(iter position, const T &x);
    /// Replace node at 'position' with subtree starting at 'from' (do not erase subtree at 'from');
    /// see above.
    template<typename iter>
    iter replace(iter position, const iterator_base &from);
    /// Replace string of siblings (plus their children) with copy of a new string (with children);
    /// see above
    sibling_iterator replace(sibling_iterator orig_begin, sibling_iterator orig_end,
                             sibling_iterator new_begin, sibling_iterator new_end);

    /// Move all children of node at 'position' to be siblings, returns position.
    template<typename iter>
    iter flatten(iter position);
    /// Move nodes in range to be children of 'position'.
    template<typename iter>
    iter reparent(iter position, sibling_iterator begin, sibling_iterator end);
    /// Move all child nodes of 'from' to be children of 'position'.
    template<typename iter>
    iter reparent(iter position, iter from);

    /// Replace node with a new node, making the old node a child of the new node.
    template<typename iter>
    iter wrap(iter position, const T &x);

    /// Move 'source' node (plus its children) to become the next sibling of 'target'.
    template<typename iter>
    iter move_after(iter target, iter source);
    /// Move 'source' node (plus its children) to become the previous sibling of 'target'.
    template<typename iter>
    iter move_before(iter target, iter source);
    sibling_iterator move_before(sibling_iterator target, sibling_iterator source);
    /// Move 'source' node (plus its children) to become the node at 'target' (erasing the node at
    /// 'target').
    template<typename iter>
    iter move_ontop(iter target, iter source);

    /// Merge with other tree, creating new branches and leaves only if they are not already
    /// present.
    void merge(sibling_iterator, sibling_iterator, sibling_iterator, sibling_iterator,
               bool duplicate_leaves = false);
    /// Sort (std::sort only moves values of nodes, this one moves children as well).
    void sort(sibling_iterator from, sibling_iterator to, bool deep = false);
    template<class StrictWeakOrdering>
    void sort(sibling_iterator from, sibling_iterator to, StrictWeakOrdering comp,
              bool deep = false);
    /// Compare two ranges of nodes (compares nodes as well as tree structure).
    template<typename iter>
    bool equal(const iter &one, const iter &two, const iter &three) const;
    template<typename iter, class BinaryPredicate>
    bool equal(const iter &one, const iter &two, const iter &three, BinaryPredicate) const;
    template<typename iter>
    bool equal_subtree(const iter &one, const iter &two) const;
    template<typename iter, class BinaryPredicate>
    bool equal_subtree(const iter &one, const iter &two, BinaryPredicate) const;
    /// Extract a new tree formed by the range of siblings plus all their children.
    tree subtree(sibling_iterator from, sibling_iterator to) const;
    void subtree(tree &, sibling_iterator from, sibling_iterator to) const;
    /// Exchange the node (plus subtree) with its sibling node (do nothing if no sibling present).
    void swap(sibling_iterator it);
    /// Exchange two nodes (plus subtrees)
    void swap(iterator, iterator);

    /// Count the total number of nodes.
    int size() const;
    /// Count the total number of nodes below the indicated node (plus one).
    int size(const iterator_base &) const;
    /// Check if tree is empty.
    bool empty() const;
    /// Compute the depth to the root.
    int depth(const iterator_base &) const;
    /// Determine the maximal depth of the tree.
    int max_depth() const;
    /// Determine the maximal depth of the tree below a given one.
    int max_depth(const iterator_base &) const;
    /// Count the number of children of node at position.
    static unsigned int number_of_children(const iterator_base &);
    /// Count the number of 'next' siblings of node at iterator.
    unsigned int number_of_siblings(const iterator_base &) const;
    /// Determine whether node at position is in the subtrees with root in the range.
    bool is_in_subtree(const iterator_base &position, const iterator_base &begin,
                       const iterator_base &end) const;
    /// Determine whether the iterator is an 'end' iterator and thus not actually pointing to a
    /// node.
    bool is_valid(const iterator_base &) const;

    /// Determine the index of a node in the range of siblings to which it belongs.
    unsigned int index(sibling_iterator it) const;
    /// Inverse of 'index': return the n-th child of the node at position.
    sibling_iterator child(const iterator_base &position, unsigned int) const;

    /// Comparator class for iterators (compares pointer values; why doesn't this work
    /// automatically?)
    class iterator_base_less
    {
    public:
        bool operator()(const typename tree<T, tree_node_allocator>::iterator_base &one,
                        const typename tree<T, tree_node_allocator>::iterator_base &two) const
        {
            return one.node < two.node;
        }
    };
    tree_node *head,
            *feet; // head/feet are always dummy; if an iterator points to them it is invalid
private:
    tree_node_allocator alloc_;
    void head_initialise_();
    void copy_(const tree<T, tree_node_allocator> &other);

    /// Comparator class for two nodes of a tree (used for sorting and searching).
    template<class StrictWeakOrdering>
    class compare_nodes
    {
    public:
        compare_nodes(StrictWeakOrdering comp) : comp_(comp){};

        bool operator()(const tree_node *a, const tree_node *b)
        {
            static StrictWeakOrdering comp;
            return comp(a->data, b->data);
        }

    private:
        StrictWeakOrdering comp_;
    };
};

// template <class T, class tree_node_allocator>
// class iterator_base_less {
// public:
//    bool operator()(const typename tree<T, tree_node_allocator>::iterator_base& one,
//                  const typename tree<T, tree_node_allocator>::iterator_base& two) const
//       {
//       txtout << "operatorclass<" << one.node < two.node << std::endl;
//       return one.node < two.node;
//       }
//};

// template <class T, class tree_node_allocator>
// bool operator<(const typename tree<T, tree_node_allocator>::iterator& one,
//                const typename tree<T, tree_node_allocator>::iterator& two)
//    {
//    txtout << "operator< " << one.node < two.node << std::endl;
//    if(one.node < two.node) return true;
//    return false;
//    }
//
// template <class T, class tree_node_allocator>
// bool operator==(const typename tree<T, tree_node_allocator>::iterator& one,
//                const typename tree<T, tree_node_allocator>::iterator& two)
//    {
//    txtout << "operator== " << one.node == two.node << std::endl;
//    if(one.node == two.node) return true;
//    return false;
//    }
//
// template <class T, class tree_node_allocator>
// bool operator>(const typename tree<T, tree_node_allocator>::iterator_base& one,
//                const typename tree<T, tree_node_allocator>::iterator_base& two)
//    {
//    txtout << "operator> " << one.node < two.node << std::endl;
//    if(one.node > two.node) return true;
//    return false;
//    }

// Tree

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::tree()
{
    head_initialise_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::tree(const T &x)
{
    head_initialise_();
    set_head(x);
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::tree(const iterator_base &other)
{
    head_initialise_();
    set_head((*other));
    replace(begin(), other);
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::~tree()
{
    clear();
    alloc_.deallocate(head, 1);
    alloc_.deallocate(feet, 1);
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::head_initialise_()
{
    head = alloc_.allocate(1);
    feet = alloc_.allocate(1);

    head->parent = nullptr;
    head->first_child = nullptr;
    head->last_child = nullptr;
    head->prev_sibling = nullptr; // head;
    head->next_sibling = feet; // head;

    feet->parent = nullptr;
    feet->first_child = nullptr;
    feet->last_child = nullptr;
    feet->prev_sibling = head;
    feet->next_sibling = nullptr;
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::operator=(const tree<T, tree_node_allocator> &other)
{
    copy_(other);
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::tree(const tree<T, tree_node_allocator> &other)
{
    head_initialise_();
    copy_(other);
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::copy_(const tree<T, tree_node_allocator> &other)
{
    clear();
    pre_order_iterator it = other.begin(), to = begin();
    while (it != other.end()) {
        to = insert(to, (*it));
        it.skip_children();
        ++it;
    }
    to = begin();
    it = other.begin();
    while (it != other.end()) {
        to = replace(to, it);
        to.skip_children();
        it.skip_children();
        ++to;
        ++it;
    }
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::clear()
{
    if (head)
        while (head->next_sibling != feet)
            erase(pre_order_iterator(head->next_sibling));
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::erase_children(const iterator_base &it)
{
    // std::cout << "erase_children " << it.node << std::endl;
    if (it.node == nullptr)
        return;

    tree_node *cur = it.node->first_child;
    tree_node *prev = nullptr;

    while (cur != nullptr) {
        prev = cur;
        cur = cur->next_sibling;
        erase_children(pre_order_iterator(prev));
        kp::destructor(&prev->data);
        alloc_.deallocate(prev, 1);
    }
    it.node->first_child = nullptr;
    it.node->last_child = nullptr;
    // std::cout << "exit" << std::endl;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::erase(iter it)
{
    tree_node *cur = it.node;
    assert(cur != head);
    iter ret = it;
    ret.skip_children();
    ++ret;
    erase_children(it);
    if (cur->prev_sibling == nullptr) {
        cur->parent->first_child = cur->next_sibling;
    } else {
        cur->prev_sibling->next_sibling = cur->next_sibling;
    }
    if (cur->next_sibling == nullptr) {
        cur->parent->last_child = cur->prev_sibling;
    } else {
        cur->next_sibling->prev_sibling = cur->prev_sibling;
    }

    kp::destructor(&cur->data);
    alloc_.deallocate(cur, 1);
    return ret;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator
tree<T, tree_node_allocator>::begin() const
{
    return pre_order_iterator(head->next_sibling);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator tree<T, tree_node_allocator>::end() const
{
    return pre_order_iterator(feet);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::breadth_first_queued_iterator
tree<T, tree_node_allocator>::begin_breadth_first() const
{
    return breadth_first_queued_iterator(head->next_sibling);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::breadth_first_queued_iterator
tree<T, tree_node_allocator>::end_breadth_first() const
{
    return breadth_first_queued_iterator();
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator
tree<T, tree_node_allocator>::begin_post() const
{
    tree_node *tmp = head->next_sibling;
    if (tmp != feet) {
        while (tmp->first_child)
            tmp = tmp->first_child;
    }
    return post_order_iterator(tmp);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator
tree<T, tree_node_allocator>::end_post() const
{
    return post_order_iterator(feet);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator
tree<T, tree_node_allocator>::begin_fixed(const iterator_base &pos, unsigned int dp) const
{
    tree_node *tmp = pos.node;
    unsigned int curdepth = 0;
    while (curdepth < dp) { // go down one level
        while (tmp->first_child == 0) {
            if (tmp->next_sibling == 0) {
                // try to walk up and then right again
                do {
                    tmp = tmp->parent;
                    if (tmp == 0)
                        throw std::range_error("tree: begin_fixed out of range");
                    --curdepth;
                } while (tmp->next_sibling == 0);
            }
            tmp = tmp->next_sibling;
        }
        tmp = tmp->first_child;
        ++curdepth;
    }
    return tmp;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator
tree<T, tree_node_allocator>::end_fixed(const iterator_base &pos, unsigned int dp) const
{
    assert(1 == 0); // FIXME: not correct yet: use is_valid() as a temporary workaround
    tree_node *tmp = pos.node;
    unsigned int curdepth = 1;
    while (curdepth < dp) { // go down one level
        while (tmp->first_child == 0) {
            tmp = tmp->next_sibling;
            if (tmp == 0)
                throw std::range_error("tree: end_fixed out of range");
        }
        tmp = tmp->first_child;
        ++curdepth;
    }
    return tmp;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::begin(const iterator_base &pos) const
{
    assert(pos.node != nullptr);
    if (pos.node->first_child == nullptr) {
        return end(pos);
    }
    return pos.node->first_child;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::end(const iterator_base &pos) const
{
    sibling_iterator ret(nullptr);
    ret.parent_ = pos.node;
    return ret;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator
tree<T, tree_node_allocator>::begin_leaf() const
{
    tree_node *tmp = head->next_sibling;
    if (tmp != feet) {
        while (tmp->first_child)
            tmp = tmp->first_child;
    }
    return leaf_iterator(tmp);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator tree<T, tree_node_allocator>::end_leaf() const
{
    return leaf_iterator(feet);
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::parent(iter position)
{
    assert(position.node != 0);
    return iter(position.node->parent);
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::previous_sibling(iter position) const
{
    assert(position.node != 0);
    iter ret(position);
    ret.node = position.node->prev_sibling;
    return ret;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::next_sibling(iter position) const
{
    assert(position.node != 0);
    iter ret(position);
    ret.node = position.node->next_sibling;
    return ret;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::next_at_same_depth(iter position) const
{
    assert(position.node != 0);
    iter ret(position);

    if (position.node->next_sibling) {
        ret.node = position.node->next_sibling;
    } else {
        int relative_depth = 0;
    upper:
        do {
            ret.node = ret.node->parent;
            if (ret.node == 0)
                return ret;
            --relative_depth;
        } while (ret.node->next_sibling == 0);
    lower:
        ret.node = ret.node->next_sibling;
        while (ret.node->first_child == 0) {
            if (ret.node->next_sibling == 0)
                goto upper;
            ret.node = ret.node->next_sibling;
            if (ret.node == 0)
                return ret;
        }
        while (relative_depth < 0 && ret.node->first_child != 0) {
            ret.node = ret.node->first_child;
            ++relative_depth;
        }
        if (relative_depth < 0) {
            if (ret.node->next_sibling == 0)
                goto upper;
            else
                goto lower;
        }
    }
    return ret;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::append_child(iter position)
{
    assert(position.node != head);
    assert(position.node);

    tree_node *tmp = alloc_.allocate(1, 0);
    kp::constructor(&tmp->data);
    tmp->first_child = 0;
    tmp->last_child = 0;

    tmp->parent = position.node;
    if (position.node->last_child != 0) {
        position.node->last_child->next_sibling = tmp;
    } else {
        position.node->first_child = tmp;
    }
    tmp->prev_sibling = position.node->last_child;
    position.node->last_child = tmp;
    tmp->next_sibling = 0;
    return tmp;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::prepend_child(iter position)
{
    assert(position.node != head);
    assert(position.node);

    tree_node *tmp = alloc_.allocate(1, 0);
    kp::constructor(&tmp->data);
    tmp->first_child = 0;
    tmp->last_child = 0;

    tmp->parent = position.node;
    if (position.node->first_child != 0) {
        position.node->first_child->prev_sibling = tmp;
    } else {
        position.node->last_child = tmp;
    }
    tmp->next_sibling = position.node->first_child;
    position.node->prev_child = tmp;
    tmp->prev_sibling = 0;
    return tmp;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::append_child(iter position, const T &x)
{
    // If your program fails here you probably used 'append_child' to add the top
    // node to an empty tree. From version 1.45 the top element should be added
    // using 'insert'. See the documentation for further information, and sorry about
    // the API change.
    assert(position.node != head);
    assert(position.node);

    tree_node *tmp = alloc_.allocate(1);
    kp::constructor(&tmp->data, x);
    tmp->first_child = nullptr;
    tmp->last_child = nullptr;

    tmp->parent = position.node;
    if (position.node->last_child != nullptr) {
        position.node->last_child->next_sibling = tmp;
    } else {
        position.node->first_child = tmp;
    }
    tmp->prev_sibling = position.node->last_child;
    position.node->last_child = tmp;
    tmp->next_sibling = nullptr;
    return tmp;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::prepend_child(iter position, const T &x)
{
    assert(position.node != head);
    assert(position.node);

    tree_node *tmp = alloc_.allocate(1, 0);
    kp::constructor(&tmp->data, x);
    tmp->first_child = 0;
    tmp->last_child = 0;

    tmp->parent = position.node;
    if (position.node->first_child != 0) {
        position.node->first_child->prev_sibling = tmp;
    } else {
        position.node->last_child = tmp;
    }
    tmp->next_sibling = position.node->first_child;
    position.node->first_child = tmp;
    tmp->prev_sibling = 0;
    return tmp;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::append_child(iter position, iter other)
{
    assert(position.node != head);
    assert(position.node);

    sibling_iterator aargh = append_child(position, value_type());
    return replace(aargh, other);
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::prepend_child(iter position, iter other)
{
    assert(position.node != head);
    assert(position.node);

    sibling_iterator aargh = prepend_child(position, value_type());
    return replace(aargh, other);
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::append_children(iter position, sibling_iterator from,
                                                   sibling_iterator to)
{
    assert(position.node != head);
    assert(position.node);

    iter ret = from;

    while (from != to) {
        insert_subtree(position.end(), from);
        ++from;
    }
    return ret;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::prepend_children(iter position, sibling_iterator from,
                                                    sibling_iterator to)
{
    assert(position.node != head);
    assert(position.node);

    iter ret = from;

    while (from != to) {
        insert_subtree(position.begin(), from);
        ++from;
    }
    return ret;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator
tree<T, tree_node_allocator>::set_head(const T &x)
{
    assert(head->next_sibling == feet);
    return insert(iterator(feet), x);
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::insert(iter position, const T &x)
{
    if (position.node == nullptr) {
        position.node = feet; // Backward compatibility: when calling insert on a null node,
                              // insert before the feet.
    }
    tree_node *tmp = alloc_.allocate(1);
    kp::constructor(&tmp->data, x);
    tmp->first_child = nullptr;
    tmp->last_child = nullptr;

    tmp->parent = position.node->parent;
    tmp->next_sibling = position.node;
    tmp->prev_sibling = position.node->prev_sibling;
    position.node->prev_sibling = tmp;

    if (tmp->prev_sibling == nullptr) {
        if (tmp->parent) // when inserting nodes at the head, there is no parent
            tmp->parent->first_child = tmp;
    } else
        tmp->prev_sibling->next_sibling = tmp;
    return tmp;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::insert(sibling_iterator position, const T &x)
{
    tree_node *tmp = alloc_.allocate(1, nullptr);
    kp::constructor(&tmp->data, x);
    tmp->first_child = nullptr;
    tmp->last_child = nullptr;

    tmp->next_sibling = position.node;
    if (position.node == nullptr) { // iterator points to end of a subtree
        tmp->parent = position.parent_;
        tmp->prev_sibling = position.range_last();
        tmp->parent->last_child = tmp;
    } else {
        tmp->parent = position.node->parent;
        tmp->prev_sibling = position.node->prev_sibling;
        position.node->prev_sibling = tmp;
    }

    if (tmp->prev_sibling == nullptr) {
        if (tmp->parent) // when inserting nodes at the head, there is no parent
            tmp->parent->first_child = tmp;
    } else
        tmp->prev_sibling->next_sibling = tmp;
    return tmp;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::insert_after(iter position, const T &x)
{
    tree_node *tmp = alloc_.allocate(1, nullptr);
    kp::constructor(&tmp->data, x);
    tmp->first_child = nullptr;
    tmp->last_child = nullptr;

    tmp->parent = position.node->parent;
    tmp->prev_sibling = position.node;
    tmp->next_sibling = position.node->next_sibling;
    position.node->next_sibling = tmp;

    if (tmp->next_sibling == nullptr) {
        if (tmp->parent) // when inserting nodes at the head, there is no parent
            tmp->parent->last_child = tmp;
    } else {
        tmp->next_sibling->prev_sibling = tmp;
    }
    return tmp;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::insert_subtree(iter position, const iterator_base &subtree)
{
    // insert dummy
    iter it = insert(position, value_type());
    // replace dummy with subtree
    return replace(it, subtree);
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::insert_subtree_after(iter position, const iterator_base &subtree)
{
    // insert dummy
    iter it = insert_after(position, value_type());
    // replace dummy with subtree
    return replace(it, subtree);
}

// template <class T, class tree_node_allocator>
// template <class iter>
// iter tree<T, tree_node_allocator>::insert_subtree(sibling_iterator position, iter subtree)
//    {
//    // insert dummy
//    iter it(insert(position, value_type()));
//    // replace dummy with subtree
//    return replace(it, subtree);
//    }

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::replace(iter position, const T &x)
{
    kp::destructor(&position.node->data);
    kp::constructor(&position.node->data, x);
    return position;
}

template<class T, class tree_node_allocator>
template<class iter>
iter tree<T, tree_node_allocator>::replace(iter position, const iterator_base &from)
{
    assert(position.node != head);
    tree_node *current_from = from.node;
    tree_node *start_from = from.node;
    tree_node *current_to = position.node;

    // replace the node at position with head of the replacement tree at from
    // std::cout << "warning!" << position.node << std::endl;
    erase_children(position);
    // std::cout << "no warning!" << std::endl;
    tree_node *tmp = alloc_.allocate(1, nullptr);
    kp::constructor(&tmp->data, (*from));
    tmp->first_child = nullptr;
    tmp->last_child = nullptr;
    if (current_to->prev_sibling == nullptr) {
        if (current_to->parent != nullptr)
            current_to->parent->first_child = tmp;
    } else {
        current_to->prev_sibling->next_sibling = tmp;
    }
    tmp->prev_sibling = current_to->prev_sibling;
    if (current_to->next_sibling == nullptr) {
        if (current_to->parent != nullptr)
            current_to->parent->last_child = tmp;
    } else {
        current_to->next_sibling->prev_sibling = tmp;
    }
    tmp->next_sibling = current_to->next_sibling;
    tmp->parent = current_to->parent;
    kp::destructor(&current_to->data);
    alloc_.deallocate(current_to, 1);
    current_to = tmp;

    // only at this stage can we fix 'last'
    tree_node *last = from.node->next_sibling;

    pre_order_iterator toit = tmp;
    // copy all children
    do {
        assert(current_from != nullptr);
        if (current_from->first_child != nullptr) {
            current_from = current_from->first_child;
            toit = append_child(toit, current_from->data);
        } else {
            while (current_from->next_sibling == nullptr && current_from != start_from) {
                current_from = current_from->parent;
                toit = parent(toit);
                assert(current_from != nullptr);
            }
            current_from = current_from->next_sibling;
            if (current_from != last) {
                toit = append_child(parent(toit), current_from->data);
            }
        }
    } while (current_from != last);

    return current_to;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::replace(sibling_iterator orig_begin, sibling_iterator orig_end,
                                      sibling_iterator new_begin, sibling_iterator new_end)
{
    tree_node *orig_first = orig_begin.node;
    tree_node *new_first = new_begin.node;
    tree_node *orig_last = orig_first;
    while ((++orig_begin) != orig_end)
        orig_last = orig_last->next_sibling;
    tree_node *new_last = new_first;
    while ((++new_begin) != new_end)
        new_last = new_last->next_sibling;

    // insert all siblings in new_first..new_last before orig_first
    bool first = true;
    pre_order_iterator ret;
    while (1 == 1) {
        pre_order_iterator tt =
                insert_subtree(pre_order_iterator(orig_first), pre_order_iterator(new_first));
        if (first) {
            ret = tt;
            first = false;
        }
        if (new_first == new_last)
            break;
        new_first = new_first->next_sibling;
    }

    // erase old range of siblings
    bool last = false;
    tree_node *next = orig_first;
    while (1 == 1) {
        if (next == orig_last)
            last = true;
        next = next->next_sibling;
        erase((pre_order_iterator)orig_first);
        if (last)
            break;
        orig_first = next;
    }
    return ret;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::flatten(iter position)
{
    if (position.node->first_child == nullptr)
        return position;

    tree_node *tmp = position.node->first_child;
    while (tmp) {
        tmp->parent = position.node->parent;
        tmp = tmp->next_sibling;
    }
    if (position.node->next_sibling) {
        position.node->last_child->next_sibling = position.node->next_sibling;
        position.node->next_sibling->prev_sibling = position.node->last_child;
    } else {
        position.node->parent->last_child = position.node->last_child;
    }
    position.node->next_sibling = position.node->first_child;
    position.node->next_sibling->prev_sibling = position.node;
    position.node->first_child = nullptr;
    position.node->last_child = nullptr;

    return position;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::reparent(iter position, sibling_iterator begin,
                                            sibling_iterator end)
{
    tree_node *first = begin.node;
    tree_node *last = first;

    assert(first != position.node);

    if (begin == end)
        return begin;
    // determine last node
    while ((++begin) != end) {
        last = last->next_sibling;
    }
    // move subtree
    if (first->prev_sibling == nullptr) {
        first->parent->first_child = last->next_sibling;
    } else {
        first->prev_sibling->next_sibling = last->next_sibling;
    }
    if (last->next_sibling == nullptr) {
        last->parent->last_child = first->prev_sibling;
    } else {
        last->next_sibling->prev_sibling = first->prev_sibling;
    }
    if (position.node->first_child == nullptr) {
        position.node->first_child = first;
        position.node->last_child = last;
        first->prev_sibling = nullptr;
    } else {
        position.node->last_child->next_sibling = first;
        first->prev_sibling = position.node->last_child;
        position.node->last_child = last;
    }
    last->next_sibling = nullptr;

    tree_node *pos = first;
    while (1 == 1) {
        pos->parent = position.node;
        if (pos == last)
            break;
        pos = pos->next_sibling;
    }

    return first;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::reparent(iter position, iter from)
{
    if (from.node->first_child == nullptr)
        return position;
    return reparent(position, from.node->first_child, end(from));
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::wrap(iter position, const T &x)
{
    assert(position.node != nullptr);
    sibling_iterator fr = position, to = position;
    ++to;
    iter ret = insert(position, x);
    reparent(ret, fr, to);
    return ret;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::move_after(iter target, iter source)
{
    tree_node *dst = target.node;
    tree_node *src = source.node;
    assert(dst);
    assert(src);

    if (dst == src)
        return source;
    if (dst->next_sibling)
        if (dst->next_sibling == src) // already in the right spot
            return source;

    // take src out of the tree
    if (src->prev_sibling != nullptr)
        src->prev_sibling->next_sibling = src->next_sibling;
    else
        src->parent->first_child = src->next_sibling;
    if (src->next_sibling != nullptr)
        src->next_sibling->prev_sibling = src->prev_sibling;
    else
        src->parent->last_child = src->prev_sibling;

    // connect it to the new point
    if (dst->next_sibling != nullptr)
        dst->next_sibling->prev_sibling = src;
    else
        dst->parent->last_child = src;
    src->next_sibling = dst->next_sibling;
    dst->next_sibling = src;
    src->prev_sibling = dst;
    src->parent = dst->parent;
    return src;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::move_before(iter target, iter source)
{
    tree_node *dst = target.node;
    tree_node *src = source.node;
    assert(dst);
    assert(src);

    if (dst == src)
        return source;
    if (dst->prev_sibling)
        if (dst->prev_sibling == src) // already in the right spot
            return source;

    // take src out of the tree
    if (src->prev_sibling != nullptr)
        src->prev_sibling->next_sibling = src->next_sibling;
    else
        src->parent->first_child = src->next_sibling;
    if (src->next_sibling != nullptr)
        src->next_sibling->prev_sibling = src->prev_sibling;
    else
        src->parent->last_child = src->prev_sibling;

    // connect it to the new point
    if (dst->prev_sibling != nullptr)
        dst->prev_sibling->next_sibling = src;
    else
        dst->parent->first_child = src;
    src->prev_sibling = dst->prev_sibling;
    dst->prev_sibling = src;
    src->next_sibling = dst;
    src->parent = dst->parent;
    return src;
}

// specialisation for sibling_iterators
template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::move_before(sibling_iterator target, sibling_iterator source)
{
    tree_node *dst = target.node;
    tree_node *src = source.node;
    tree_node *dst_prev_sibling;
    if (dst == nullptr) { // must then be an end iterator
        dst_prev_sibling = target.parent_->last_child;
        assert(dst_prev_sibling);
    } else
        dst_prev_sibling = dst->prev_sibling;
    assert(src);

    if (dst == src)
        return source;
    if (dst_prev_sibling)
        if (dst_prev_sibling == src) // already in the right spot
            return source;

    // take src out of the tree
    if (src->prev_sibling != nullptr)
        src->prev_sibling->next_sibling = src->next_sibling;
    else
        src->parent->first_child = src->next_sibling;
    if (src->next_sibling != nullptr)
        src->next_sibling->prev_sibling = src->prev_sibling;
    else
        src->parent->last_child = src->prev_sibling;

    // connect it to the new point
    if (dst_prev_sibling != nullptr)
        dst_prev_sibling->next_sibling = src;
    else
        target.parent_->first_child = src;
    src->prev_sibling = dst_prev_sibling;
    if (dst) {
        dst->prev_sibling = src;
        src->parent = dst->parent;
    }
    src->next_sibling = dst;
    return src;
}

template<class T, class tree_node_allocator>
template<typename iter>
iter tree<T, tree_node_allocator>::move_ontop(iter target, iter source)
{
    tree_node *dst = target.node;
    tree_node *src = source.node;
    assert(dst);
    assert(src);

    if (dst == src)
        return source;

    // remember connection points
    tree_node *b_prev_sibling = dst->prev_sibling;
    tree_node *b_next_sibling = dst->next_sibling;
    tree_node *b_parent = dst->parent;

    // remove target
    erase(target);

    // take src out of the tree
    if (src->prev_sibling != nullptr)
        src->prev_sibling->next_sibling = src->next_sibling;
    else
        src->parent->first_child = src->next_sibling;
    if (src->next_sibling != nullptr)
        src->next_sibling->prev_sibling = src->prev_sibling;
    else
        src->parent->last_child = src->prev_sibling;

    // connect it to the new point
    if (b_prev_sibling != nullptr)
        b_prev_sibling->next_sibling = src;
    else
        b_parent->first_child = src;
    if (b_next_sibling != nullptr)
        b_next_sibling->prev_sibling = src;
    else
        b_parent->last_child = src;
    src->prev_sibling = b_prev_sibling;
    src->next_sibling = b_next_sibling;
    src->parent = b_parent;
    return src;
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::merge(sibling_iterator to1, sibling_iterator to2,
                                         sibling_iterator from1, sibling_iterator from2,
                                         bool duplicate_leaves)
{
    sibling_iterator fnd;
    while (from1 != from2) {
        if ((fnd = std::find(to1, to2, (*from1))) != to2) { // element found
            if (from1.begin() == from1.end()) { // full depth reached
                if (duplicate_leaves)
                    append_child(parent(to1), (*from1));
            } else { // descend further
                merge(fnd.begin(), fnd.end(), from1.begin(), from1.end(), duplicate_leaves);
            }
        } else { // element missing
            insert_subtree(to2, from1);
        }
        ++from1;
    }
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::sort(sibling_iterator from, sibling_iterator to, bool deep)
{
    std::less<T> comp;
    sort(from, to, comp, deep);
}

template<class T, class tree_node_allocator>
template<class StrictWeakOrdering>
void tree<T, tree_node_allocator>::sort(sibling_iterator from, sibling_iterator to,
                                        StrictWeakOrdering comp, bool deep)
{
    if (from == to)
        return;
    // make list of sorted nodes
    // CHECK: if multiset stores equivalent nodes in the order in which they
    // are inserted, then this routine should be called 'stable_sort'.
    std::multiset<tree_node *, compare_nodes<StrictWeakOrdering>> nodes(comp);
    sibling_iterator it = from, it2 = to;
    while (it != to) {
        nodes.insert(it.node);
        ++it;
    }
    // reassemble
    --it2;

    // prev and next are the nodes before and after the sorted range
    tree_node *prev = from.node->prev_sibling;
    tree_node *next = it2.node->next_sibling;
    typename std::multiset<tree_node *, compare_nodes<StrictWeakOrdering>>::iterator
            nit = nodes.begin(),
            eit = nodes.end();
    if (prev == nullptr) {
        if ((*nit)->parent
            != nullptr) // to catch "sorting the head" situations, when there is no parent
            (*nit)->parent->first_child = (*nit);
    } else
        prev->next_sibling = (*nit);

    --eit;
    while (nit != eit) {
        (*nit)->prev_sibling = prev;
        if (prev)
            prev->next_sibling = (*nit);
        prev = (*nit);
        ++nit;
    }
    // prev now points to the last-but-one node in the sorted range
    if (prev)
        prev->next_sibling = (*eit);

    // eit points to the last node in the sorted range.
    (*eit)->next_sibling = next;
    (*eit)->prev_sibling = prev; // missed in the loop above
    if (next == nullptr) {
        if ((*eit)->parent
            != nullptr) // to catch "sorting the head" situations, when there is no parent
            (*eit)->parent->last_child = (*eit);
    } else
        next->prev_sibling = (*eit);

    if (deep) { // sort the children of each node too
        sibling_iterator bcs(*nodes.begin());
        sibling_iterator ecs(*eit);
        ++ecs;
        while (bcs != ecs) {
            sort(begin(bcs), end(bcs), comp, deep);
            ++bcs;
        }
    }
}

template<class T, class tree_node_allocator>
template<typename iter>
bool tree<T, tree_node_allocator>::equal(const iter &one_, const iter &two,
                                         const iter &three_) const
{
    std::equal_to<T> comp;
    return equal(one_, two, three_, comp);
}

template<class T, class tree_node_allocator>
template<typename iter>
bool tree<T, tree_node_allocator>::equal_subtree(const iter &one_, const iter &two_) const
{
    std::equal_to<T> comp;
    return equal_subtree(one_, two_, comp);
}

template<class T, class tree_node_allocator>
template<typename iter, class BinaryPredicate>
bool tree<T, tree_node_allocator>::equal(const iter &one_, const iter &two, const iter &three_,
                                         BinaryPredicate fun) const
{
    pre_order_iterator one(one_), three(three_);

    // if(one==two && is_valid(three) && three.number_of_children()!=nullptr)
    //    return false;
    while (one != two && is_valid(three)) {
        if (!fun(*one, *three))
            return false;
        if (one.number_of_children() != three.number_of_children())
            return false;
        ++one;
        ++three;
    }
    return true;
}

template<class T, class tree_node_allocator>
template<typename iter, class BinaryPredicate>
bool tree<T, tree_node_allocator>::equal_subtree(const iter &one_, const iter &two_,
                                                 BinaryPredicate fun) const
{
    pre_order_iterator one(one_), two(two_);

    if (!fun(*one, *two))
        return false;
    if (number_of_children(one) != number_of_children(two))
        return false;
    return equal(begin(one), end(one), begin(two), fun);
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator> tree<T, tree_node_allocator>::subtree(sibling_iterator from,
                                                                   sibling_iterator to) const
{
    tree tmp;
    tmp.set_head(value_type());
    tmp.replace(tmp.begin(), tmp.end(), from, to);
    return tmp;
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::subtree(tree &tmp, sibling_iterator from,
                                           sibling_iterator to) const
{
    tmp.set_head(value_type());
    tmp.replace(tmp.begin(), tmp.end(), from, to);
}

template<class T, class tree_node_allocator>
int tree<T, tree_node_allocator>::size() const
{
    int i = 0;
    pre_order_iterator it = begin(), eit = end();
    while (it != eit) {
        ++i;
        ++it;
    }
    return i;
}

template<class T, class tree_node_allocator>
int tree<T, tree_node_allocator>::size(const iterator_base &top) const
{
    int i = 0;
    pre_order_iterator it = top, eit = top;
    eit.skip_children();
    ++eit;
    while (it != eit) {
        ++i;
        ++it;
    }
    return i;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::empty() const
{
    pre_order_iterator it = begin(), eit = end();
    return (it == eit);
}

template<class T, class tree_node_allocator>
int tree<T, tree_node_allocator>::depth(const iterator_base &it) const
{
    tree_node *pos = it.node;
    assert(pos != nullptr);
    int ret = 0;
    while (pos->parent != nullptr) {
        pos = pos->parent;
        ++ret;
    }
    return ret;
}

template<class T, class tree_node_allocator>
int tree<T, tree_node_allocator>::max_depth() const
{
    return max_depth(begin());
}

template<class T, class tree_node_allocator>
int tree<T, tree_node_allocator>::max_depth(const iterator_base &pos) const
{
    tree_node *tmp = pos.node;
    int curdepth = 0, maxdepth = 0;
    while (true) { // try to walk the bottom of the tree
        while (tmp->first_child == 0) {
            if (tmp == pos.node)
                return maxdepth;
            if (tmp->next_sibling == 0) {
                // try to walk up and then right again
                do {
                    tmp = tmp->parent;
                    if (tmp == 0)
                        return maxdepth;
                    --curdepth;
                } while (tmp->next_sibling == 0);
            }
            if (tmp == pos.node)
                return maxdepth;
            tmp = tmp->next_sibling;
        }
        tmp = tmp->first_child;
        ++curdepth;
        maxdepth = std::max(curdepth, maxdepth);
    }
}

template<class T, class tree_node_allocator>
unsigned int tree<T, tree_node_allocator>::number_of_children(const iterator_base &it)
{
    tree_node *pos = it.node->first_child;
    if (pos == 0)
        return 0;

    unsigned int ret = 1;
    //   while(pos!=it.node->last_child) {
    //      ++ret;
    //      pos=pos->next_sibling;
    //      }
    while ((pos = pos->next_sibling))
        ++ret;
    return ret;
}

template<class T, class tree_node_allocator>
unsigned int tree<T, tree_node_allocator>::number_of_siblings(const iterator_base &it) const
{
    tree_node *pos = it.node;
    unsigned int ret = 0;
    // count forward
    while (pos->next_sibling && pos->next_sibling != head && pos->next_sibling != feet) {
        ++ret;
        pos = pos->next_sibling;
    }
    // count backward
    pos = it.node;
    while (pos->prev_sibling && pos->prev_sibling != head && pos->prev_sibling != feet) {
        ++ret;
        pos = pos->prev_sibling;
    }

    return ret;
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::swap(sibling_iterator it)
{
    tree_node *nxt = it.node->next_sibling;
    if (nxt) {
        if (it.node->prev_sibling)
            it.node->prev_sibling->next_sibling = nxt;
        else
            it.node->parent->first_child = nxt;
        nxt->prev_sibling = it.node->prev_sibling;
        tree_node *nxtnxt = nxt->next_sibling;
        if (nxtnxt)
            nxtnxt->prev_sibling = it.node;
        else
            it.node->parent->last_child = it.node;
        nxt->next_sibling = it.node;
        it.node->prev_sibling = nxt;
        it.node->next_sibling = nxtnxt;
    }
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::swap(iterator one, iterator two)
{
    // if one and two are adjacent siblings, use the sibling swap
    if (one.node->next_sibling == two.node)
        swap(one);
    else if (two.node->next_sibling == one.node)
        swap(two);
    else {
        tree_node *nxt1 = one.node->next_sibling;
        tree_node *nxt2 = two.node->next_sibling;
        tree_node *pre1 = one.node->prev_sibling;
        tree_node *pre2 = two.node->prev_sibling;
        tree_node *par1 = one.node->parent;
        tree_node *par2 = two.node->parent;

        // reconnect
        one.node->parent = par2;
        one.node->next_sibling = nxt2;
        if (nxt2)
            nxt2->prev_sibling = one.node;
        else
            par2->last_child = one.node;
        one.node->prev_sibling = pre2;
        if (pre2)
            pre2->next_sibling = one.node;
        else
            par2->first_child = one.node;

        two.node->parent = par1;
        two.node->next_sibling = nxt1;
        if (nxt1)
            nxt1->prev_sibling = two.node;
        else
            par1->last_child = two.node;
        two.node->prev_sibling = pre1;
        if (pre1)
            pre1->next_sibling = two.node;
        else
            par1->first_child = two.node;
    }
}

// template <class BinaryPredicate>
// tree<T, tree_node_allocator>::iterator tree<T, tree_node_allocator>::find_subtree(
//    sibling_iterator subfrom, sibling_iterator subto, iterator from, iterator to,
//    BinaryPredicate fun) const
//    {
//    assert(1==0); // this routine is not finished yet.
//    while(from!=to) {
//       if(fun(*subfrom, *from)) {
//
//          }
//       }
//    return to;
//    }

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::is_in_subtree(const iterator_base &it,
                                                 const iterator_base &begin,
                                                 const iterator_base &end) const
{
    // FIXME: this should be optimised.
    pre_order_iterator tmp = begin;
    while (tmp != end) {
        if (tmp == it)
            return true;
        ++tmp;
    }
    return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::is_valid(const iterator_base &it) const
{
    if (it.node == 0 || it.node == feet || it.node == head)
        return false;
    else
        return true;
}

template<class T, class tree_node_allocator>
unsigned int tree<T, tree_node_allocator>::index(sibling_iterator it) const
{
    unsigned int ind = 0;
    if (it.node->parent == 0) {
        while (it.node->prev_sibling != head) {
            it.node = it.node->prev_sibling;
            ++ind;
        }
    } else {
        while (it.node->prev_sibling != 0) {
            it.node = it.node->prev_sibling;
            ++ind;
        }
    }
    return ind;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::child(const iterator_base &it, unsigned int num) const
{
    tree_node *tmp = it.node->first_child;
    while (num--) {
        assert(tmp != 0);
        tmp = tmp->next_sibling;
    }
    return tmp;
}

// Iterator base

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::iterator_base::iterator_base()
    : node(0), skip_current_children_(false)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::iterator_base::iterator_base(tree_node *tn)
    : node(tn), skip_current_children_(false)
{
}

template<class T, class tree_node_allocator>
T &tree<T, tree_node_allocator>::iterator_base::operator*() const
{
    return node->data;
}

template<class T, class tree_node_allocator>
T *tree<T, tree_node_allocator>::iterator_base::operator->() const
{
    return &(node->data);
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::post_order_iterator::operator!=(
        const post_order_iterator &other) const
{
    if (other.node != this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::post_order_iterator::operator==(
        const post_order_iterator &other) const
{
    if (other.node == this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::pre_order_iterator::operator!=(
        const pre_order_iterator &other) const
{
    if (other.node != this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::pre_order_iterator::operator==(
        const pre_order_iterator &other) const
{
    if (other.node == this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::sibling_iterator::operator!=(const sibling_iterator &other) const
{
    if (other.node != this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::sibling_iterator::operator==(const sibling_iterator &other) const
{
    if (other.node == this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::leaf_iterator::operator!=(const leaf_iterator &other) const
{
    if (other.node != this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::leaf_iterator::operator==(const leaf_iterator &other) const
{
    if (other.node == this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::iterator_base::begin() const
{
    if (node->first_child == 0)
        return end();

    sibling_iterator ret(node->first_child);
    ret.parent_ = this->node;
    return ret;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::iterator_base::end() const
{
    sibling_iterator ret(0);
    ret.parent_ = node;
    return ret;
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::iterator_base::skip_children()
{
    skip_current_children_ = true;
}

template<class T, class tree_node_allocator>
unsigned int tree<T, tree_node_allocator>::iterator_base::number_of_children() const
{
    tree_node *pos = node->first_child;
    if (pos == 0)
        return 0;

    unsigned int ret = 1;
    while (pos != node->last_child) {
        ++ret;
        pos = pos->next_sibling;
    }
    return ret;
}

// Pre-order iterator

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::pre_order_iterator::pre_order_iterator() : iterator_base(nullptr)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::pre_order_iterator::pre_order_iterator(tree_node *tn)
    : iterator_base(tn)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::pre_order_iterator::pre_order_iterator(const iterator_base &other)
    : iterator_base(other.node)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::pre_order_iterator::pre_order_iterator(const sibling_iterator &other)
    : iterator_base(other.node)
{
    if (this->node == nullptr) {
        if (other.range_last() != nullptr)
            this->node = other.range_last();
        else
            this->node = other.parent_;
        this->skip_children();
        ++(*this);
    }
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator &
tree<T, tree_node_allocator>::pre_order_iterator::operator++()
{
    assert(this->node != nullptr);
    if (!this->skip_current_children_ && this->node->first_child != nullptr) {
        this->node = this->node->first_child;
    } else {
        this->skip_current_children_ = false;
        while (this->node->next_sibling == nullptr) {
            this->node = this->node->parent;
            if (this->node == nullptr)
                return *this;
        }
        this->node = this->node->next_sibling;
    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator &
tree<T, tree_node_allocator>::pre_order_iterator::operator--()
{
    assert(this->node != 0);
    if (this->node->prev_sibling) {
        this->node = this->node->prev_sibling;
        while (this->node->last_child)
            this->node = this->node->last_child;
    } else {
        this->node = this->node->parent;
        if (this->node == 0)
            return *this;
    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator
tree<T, tree_node_allocator>::pre_order_iterator::operator++(int)
{
    pre_order_iterator copy = *this;
    ++(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator
tree<T, tree_node_allocator>::pre_order_iterator::operator--(int)
{
    pre_order_iterator copy = *this;
    --(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator &
tree<T, tree_node_allocator>::pre_order_iterator::operator+=(unsigned int num)
{
    while (num > 0) {
        ++(*this);
        --num;
    }
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::pre_order_iterator &
tree<T, tree_node_allocator>::pre_order_iterator::operator-=(unsigned int num)
{
    while (num > 0) {
        --(*this);
        --num;
    }
    return (*this);
}

// Post-order iterator

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::post_order_iterator::post_order_iterator() : iterator_base(0)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::post_order_iterator::post_order_iterator(tree_node *tn)
    : iterator_base(tn)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::post_order_iterator::post_order_iterator(const iterator_base &other)
    : iterator_base(other.node)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::post_order_iterator::post_order_iterator(
        const sibling_iterator &other)
    : iterator_base(other.node)
{
    if (this->node == 0) {
        if (other.range_last() != 0)
            this->node = other.range_last();
        else
            this->node = other.parent_;
        this->skip_children();
        ++(*this);
    }
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator &
tree<T, tree_node_allocator>::post_order_iterator::operator++()
{
    assert(this->node != 0);
    if (this->node->next_sibling == 0) {
        this->node = this->node->parent;
        this->skip_current_children_ = false;
    } else {
        this->node = this->node->next_sibling;
        if (this->skip_current_children_) {
            this->skip_current_children_ = false;
        } else {
            while (this->node->first_child)
                this->node = this->node->first_child;
        }
    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator &
tree<T, tree_node_allocator>::post_order_iterator::operator--()
{
    assert(this->node != 0);
    if (this->skip_current_children_ || this->node->last_child == 0) {
        this->skip_current_children_ = false;
        while (this->node->prev_sibling == 0)
            this->node = this->node->parent;
        this->node = this->node->prev_sibling;
    } else {
        this->node = this->node->last_child;
    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator
tree<T, tree_node_allocator>::post_order_iterator::operator++(int)
{
    post_order_iterator copy = *this;
    ++(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator
tree<T, tree_node_allocator>::post_order_iterator::operator--(int)
{
    post_order_iterator copy = *this;
    --(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator &
tree<T, tree_node_allocator>::post_order_iterator::operator+=(unsigned int num)
{
    while (num > 0) {
        ++(*this);
        --num;
    }
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::post_order_iterator &
tree<T, tree_node_allocator>::post_order_iterator::operator-=(unsigned int num)
{
    while (num > 0) {
        --(*this);
        --num;
    }
    return (*this);
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::post_order_iterator::descend_all()
{
    assert(this->node != 0);
    while (this->node->first_child)
        this->node = this->node->first_child;
}

// Breadth-first iterator

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::breadth_first_queued_iterator::breadth_first_queued_iterator()
    : iterator_base()
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::breadth_first_queued_iterator::breadth_first_queued_iterator(
        tree_node *tn)
    : iterator_base(tn)
{
    traversal_queue.push(tn);
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::breadth_first_queued_iterator::breadth_first_queued_iterator(
        const iterator_base &other)
    : iterator_base(other.node)
{
    traversal_queue.push(other.node);
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::breadth_first_queued_iterator::operator!=(
        const breadth_first_queued_iterator &other) const
{
    if (other.node != this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::breadth_first_queued_iterator::operator==(
        const breadth_first_queued_iterator &other) const
{
    if (other.node == this->node)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::breadth_first_queued_iterator &
tree<T, tree_node_allocator>::breadth_first_queued_iterator::operator++()
{
    assert(this->node != 0);

    // Add child nodes and pop current node
    sibling_iterator sib = this->begin();
    while (sib != this->end()) {
        traversal_queue.push(sib.node);
        ++sib;
    }
    traversal_queue.pop();
    if (traversal_queue.size() > 0)
        this->node = traversal_queue.front();
    else
        this->node = 0;
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::breadth_first_queued_iterator
tree<T, tree_node_allocator>::breadth_first_queued_iterator::operator++(int)
{
    breadth_first_queued_iterator copy = *this;
    ++(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::breadth_first_queued_iterator &
tree<T, tree_node_allocator>::breadth_first_queued_iterator::operator+=(unsigned int num)
{
    while (num > 0) {
        ++(*this);
        --num;
    }
    return (*this);
}

// Fixed depth iterator

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::fixed_depth_iterator::fixed_depth_iterator() : iterator_base()
{
    set_first_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::fixed_depth_iterator::fixed_depth_iterator(tree_node *tn)
    : iterator_base(tn)
{
    set_first_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::fixed_depth_iterator::fixed_depth_iterator(const iterator_base &other)
    : iterator_base(other.node)
{
    set_first_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::fixed_depth_iterator::fixed_depth_iterator(
        const sibling_iterator &other)
    : iterator_base(other.node), first_parent_(other.parent_)
{
    find_leftmost_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::fixed_depth_iterator::fixed_depth_iterator(
        const fixed_depth_iterator &other)
    : iterator_base(other.node), first_parent_(other.first_parent_)
{
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::fixed_depth_iterator::operator==(
        const fixed_depth_iterator &other) const
{
    if (other.node == this->node && other.first_parent_ == first_parent_)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
bool tree<T, tree_node_allocator>::fixed_depth_iterator::operator!=(
        const fixed_depth_iterator &other) const
{
    if (other.node != this->node || other.first_parent_ != first_parent_)
        return true;
    else
        return false;
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::fixed_depth_iterator::set_first_parent_()
{
    return; // FIXME: we do not use first_parent_ yet, and it actually needs some serious reworking
            // if it is ever to work at the 'head' level.
    first_parent_ = 0;
    if (this->node == 0)
        return;
    if (this->node->parent != 0)
        first_parent_ = this->node->parent;
    if (first_parent_)
        find_leftmost_parent_();
}

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::fixed_depth_iterator::find_leftmost_parent_()
{
    return; // FIXME: see 'set_first_parent()'
    tree_node *tmppar = first_parent_;
    while (tmppar->prev_sibling) {
        tmppar = tmppar->prev_sibling;
        if (tmppar->first_child)
            first_parent_ = tmppar;
    }
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator &
tree<T, tree_node_allocator>::fixed_depth_iterator::operator++()
{
    assert(this->node != 0);

    if (this->node->next_sibling) {
        this->node = this->node->next_sibling;
    } else {
        int relative_depth = 0;
    upper:
        do {
            this->node = this->node->parent;
            if (this->node == 0)
                return *this;
            --relative_depth;
        } while (this->node->next_sibling == 0);
    lower:
        this->node = this->node->next_sibling;
        while (this->node->first_child == 0) {
            if (this->node->next_sibling == 0)
                goto upper;
            this->node = this->node->next_sibling;
            if (this->node == 0)
                return *this;
        }
        while (relative_depth < 0 && this->node->first_child != 0) {
            this->node = this->node->first_child;
            ++relative_depth;
        }
        if (relative_depth < 0) {
            if (this->node->next_sibling == 0)
                goto upper;
            else
                goto lower;
        }
    }
    return *this;

    // if(this->node->next_sibling!=0) {
    //    this->node=this->node->next_sibling;
    //    assert(this->node!=0);
    //    if(this->node->parent==0 && this->node->next_sibling==0) // feet element
    //       this->node=0;
    //    }
    // else {
    //    tree_node *par=this->node->parent;
    //    do {
    //       par=par->next_sibling;
    //       if(par==0) { // FIXME: need to keep track of this!
    //          this->node=0;
    //          return *this;
    //          }
    //       } while(par->first_child==0);
    //    this->node=par->first_child;
    //    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator &
tree<T, tree_node_allocator>::fixed_depth_iterator::operator--()
{
    assert(this->node != 0);
    if (this->node->prev_sibling != 0) {
        this->node = this->node->prev_sibling;
        assert(this->node != 0);
        if (this->node->parent == 0 && this->node->prev_sibling == 0) // head element
            this->node = 0;
    } else {
        tree_node *par = this->node->parent;
        do {
            par = par->prev_sibling;
            if (par == 0) { // FIXME: need to keep track of this!
                this->node = 0;
                return *this;
            }
        } while (par->last_child == 0);
        this->node = par->last_child;
    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator
tree<T, tree_node_allocator>::fixed_depth_iterator::operator++(int)
{
    fixed_depth_iterator copy = *this;
    ++(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator
tree<T, tree_node_allocator>::fixed_depth_iterator::operator--(int)
{
    fixed_depth_iterator copy = *this;
    --(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator &
tree<T, tree_node_allocator>::fixed_depth_iterator::operator-=(unsigned int num)
{
    while (num > 0) {
        --(*this);
        --(num);
    }
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::fixed_depth_iterator &
tree<T, tree_node_allocator>::fixed_depth_iterator::operator+=(unsigned int num)
{
    while (num > 0) {
        ++(*this);
        --(num);
    }
    return *this;
}

// FIXME: add the other members of fixed_depth_iterator.

// Sibling iterator

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::sibling_iterator::sibling_iterator() : iterator_base()
{
    set_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::sibling_iterator::sibling_iterator(tree_node *tn) : iterator_base(tn)
{
    set_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::sibling_iterator::sibling_iterator(const iterator_base &other)
    : iterator_base(other.node)
{
    set_parent_();
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::sibling_iterator::sibling_iterator(const sibling_iterator &) =
        default;

template<class T, class tree_node_allocator>
void tree<T, tree_node_allocator>::sibling_iterator::set_parent_()
{
    parent_ = nullptr;
    if (this->node == nullptr)
        return;
    if (this->node->parent != nullptr)
        parent_ = this->node->parent;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator &
tree<T, tree_node_allocator>::sibling_iterator::operator++()
{
    if (this->node)
        this->node = this->node->next_sibling;
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator &
tree<T, tree_node_allocator>::sibling_iterator::operator--()
{
    if (this->node)
        this->node = this->node->prev_sibling;
    else {
        assert(parent_);
        this->node = parent_->last_child;
    }
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::sibling_iterator::operator++(int)
{
    sibling_iterator copy = *this;
    ++(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator
tree<T, tree_node_allocator>::sibling_iterator::operator--(int)
{
    sibling_iterator copy = *this;
    --(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator &
tree<T, tree_node_allocator>::sibling_iterator::operator+=(unsigned int num)
{
    while (num > 0) {
        ++(*this);
        --num;
    }
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::sibling_iterator &
tree<T, tree_node_allocator>::sibling_iterator::operator-=(unsigned int num)
{
    while (num > 0) {
        --(*this);
        --num;
    }
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::tree_node *
tree<T, tree_node_allocator>::sibling_iterator::range_first() const
{
    tree_node *tmp = parent_->first_child;
    return tmp;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::tree_node *
tree<T, tree_node_allocator>::sibling_iterator::range_last() const
{
    return parent_->last_child;
}

// Leaf iterator

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::leaf_iterator::leaf_iterator() : iterator_base(0)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::leaf_iterator::leaf_iterator(tree_node *tn) : iterator_base(tn)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::leaf_iterator::leaf_iterator(const iterator_base &other)
    : iterator_base(other.node)
{
}

template<class T, class tree_node_allocator>
tree<T, tree_node_allocator>::leaf_iterator::leaf_iterator(const sibling_iterator &other)
    : iterator_base(other.node)
{
    if (this->node == nullptr) {
        if (other.range_last() != nullptr)
            this->node = other.range_last();
        else
            this->node = other.parent_;
        ++(*this);
    }
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator &
tree<T, tree_node_allocator>::leaf_iterator::operator++()
{
    assert(this->node != nullptr);
    while (this->node->next_sibling == nullptr) {
        if (this->node->parent == nullptr)
            return *this;
        this->node = this->node->parent;
    }
    this->node = this->node->next_sibling;
    while (this->node->first_child)
        this->node = this->node->first_child;
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator &
tree<T, tree_node_allocator>::leaf_iterator::operator--()
{
    assert(this->node != nullptr);
    while (this->node->prev_sibling == nullptr) {
        if (this->node->parent == nullptr)
            return *this;
        this->node = this->node->parent;
    }
    this->node = this->node->prev_sibling;
    while (this->node->last_child)
        this->node = this->node->last_child;
    return *this;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator
tree<T, tree_node_allocator>::leaf_iterator::operator++(int)
{
    leaf_iterator copy = *this;
    ++(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator
tree<T, tree_node_allocator>::leaf_iterator::operator--(int)
{
    leaf_iterator copy = *this;
    --(*this);
    return copy;
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator &
tree<T, tree_node_allocator>::leaf_iterator::operator+=(unsigned int num)
{
    while (num > 0) {
        ++(*this);
        --num;
    }
    return (*this);
}

template<class T, class tree_node_allocator>
typename tree<T, tree_node_allocator>::leaf_iterator &
tree<T, tree_node_allocator>::leaf_iterator::operator-=(unsigned int num)
{
    while (num > 0) {
        --(*this);
        --num;
    }
    return (*this);
}

#endif

// Local variables:
// default-tab-width: 3
// End:
