template<typename ymd_type_, typename date_int_type_> 
class gregorian_calendar_base {
public:
  // types
  typedef ymd_type_            ymd_type;       // define a type a date split into components 
  typedef ymd_type::month_type month_type;     // define a type for representing months 
  typedef ymd_type::day_type   day_type;       // define a type for representing days 
  typedef ymd_type::year_type  year_type;      // Type to hold a stand alone year value (eg: 2002). 
  typedef date_int_type_       date_int_type;  // Define the integer type to use for internal calculations. 

  // public static functions
  unsigned short day_of_week(const ymd_type &) ;
  int week_number(const ymd_type &) ;
  date_int_type day_number(const ymd_type &) ;
  date_int_type julian_day_number(const ymd_type &) ;
  long modjulian_day_number(const ymd_type &) ;
  ymd_type from_day_number(date_int_type) ;
  ymd_type from_julian_day_number(date_int_type) ;
  ymd_type from_modjulian_day_number(long) ;
  bool is_leap_year(year_type) ;
  unsigned short end_of_month_day(year_type, month_type) ;
  ymd_type epoch() ;
  unsigned short days_in_week() ;
};