docs: def lub(self, other):
          """
          Return the least upper bound for given intervals.
  
          :param other: AbstractInterval instance
          """
          return self.__class__(
              [
                  max(self.lower, other.lower),
                  max(self.upper, other.upper),
              ],
              lower_inc=self.lower_inc if self < other else other.lower_inc,
              upper_inc=self.upper_inc if self > other else other.upper_inc,
          )