Postorder Iterator

template < typename T >
class TBinaryTreePostorderIterator
{
private:
  TBinaryTree<T>::Navigator nav_;

public:

  // constructors
  TBinaryTreePostorderIterator    ();
  ~TBinaryTreePostorderIterator   ();
  TBinaryTreePostorderIterator    (const TBinaryTreePostorderIterator& i);

  // bidirectional iterator
  // ...

} ;