Inorder Iterator

template < class Navigator >
class BinaryTreeInorderIterator
{
private:
  Navigator nav_;

public:

  // constructors
  BinaryTreeInorderIterator    ();
  ~BinaryTreeInorderIterator   ();
  BinaryTreeInorderIterator    (const BinaryTreeInorderIterator& i);
  BinaryTreeInorderIterator    (const Navigator& n); // convert Navi to Iter

  // bidirectional iterator
  // ...

} ;