code: def max_neg(self):
          '''Returns maximum negative value or None.'''
          if self.__len__() == 0:
              return ArgumentError('empty set has no maximum negative value.')
          if self.contains(0):
              return None
          negative = [interval for interval in self.intervals
                      if interval.right < 0]
          if len(negative) == 0:
              return None
          return numpy.max(list(map(lambda i: i.right, negative))f max_neg(self):
          '''Returns maximum negative value or None.'''
          if self.__len__() == 0:
              return ArgumentError('empty set has no maximum negative value.')
          if self.contains(0):
              return None
          negative = [interval for interval in self.intervals
                      if interval.right < 0]
          if len(negative) == 0:
              return None
          return numpy.max(list(map(lambda i: i.right, negative)))
docs: Returns maximum negative value or None.