code: def workdays(first_day=None):
      
      if first_day is None:
          first_day = 'Monday'
      ix = _lower_weekdays().index(first_day.lower())
      return _double_weekdays()[ix:ix+5]
docs: Returns a list of workday names.
  
      Arguments
      ---------
      first_day : str, default None
          The first day of the five-day work week. If not given, 'Monday' is
          used.
  
      Returns
      -------
      list
          A list of workday names.