namespace boost {
  class cell;

  // Compares the cell with a string assuming that the cell contains a string. Method is outside class because it take cell as the second operand. 
  bool operator>(const std::string & lhs, const cell & rhs);
}

namespace boost {
  template<typename Value> class column_iter;
  class column;

  typedef column_iter< boost::cell > column_iterator;
  typedef column_iter< const boost::cell > const_column_iterator;
}

namespace boost {
  struct cell_content_type;
}

namespace boost {
  struct document_file_format;
}

namespace boost {
  class document;
}

namespace boost {
  template<typename Value> class row_iter;
  class row;

  typedef row_iter< boost::cell > row_iterator;
  typedef row_iter< const boost::cell > const_row_iterator;
}

namespace boost {
  class sheet;
}