code: def _add_left(self, d):
          '''
          Adds the provided domino to the left end of the board.
  
          :param Domino d: domino to add
          :return: None
          :raises EndsMismatchException: if the values do not match
          '''
          if not self:
              self.board.append(d)
          elif d.first == self.left_end():
              self.board.appendleft(d.inverted())
          elif d.second == self.left_end():
              self.board.appendleft(d)
          else:
              raise dominoes.EndsMismatchException(
                  '{} cannot be added to the left of'
                  ' the board - values do not match!'.format(d)
              f _add_left(self, d):
          '''
          Adds the provided domino to the left end of the board.
  
          :param Domino d: domino to add
          :return: None
          :raises EndsMismatchException: if the values do not match
          '''
          if not self:
              self.board.append(d)
          elif d.first == self.left_end():
              self.board.appendleft(d.inverted())
          elif d.second == self.left_end():
              self.board.appendleft(d)
          else:
              raise dominoes.EndsMismatchException(
                  '{} cannot be added to the left of'
                  ' the board - values do not match!'.format(d)
              )
docs: Adds the provided domino to the left end of the board.
  
          :param Domino d: domino to add
          :return: None
          :raises EndsMismatchException: if the values do not match