tree

template <class k, class t, class compare, class less = core::less<t>>
struct tree : public set<t,less>
{
  typedef set_iterator<t> iterator;
 
  tree();

  tree(std::initializer_list<t> l);

  t& operator[](const k& key);

  void erase(const k& key);

  bool contains(const k& key) const;

  iterator find(const k& key) const;

  t* locate(const k& key) const;
};