template<typename time_type> 
class time_itr {
public:
  // types
  typedef time_type::time_duration_type time_duration_type;

  // construct/copy/destruct
  time_itr(time_type, time_duration_type);

  // public member functions
  time_itr & operator++() ;
  time_itr & operator--() ;
  time_type operator *() ;
  time_type * operator->() ;
  bool operator<(const time_type &) ;
  bool operator<=(const time_type &) ;
  bool operator!=(const time_type &) ;
  bool operator==(const time_type &) ;
  bool operator>(const time_type &) ;
  bool operator>=(const time_type &) ;
};