docs: def _increment(sign, integer_part, non_repeating_part, base):
          """
          Return an increment radix.
  
          :param int sign: -1, 0, or 1 as appropriate
          :param integer_part: the integer part
          :type integer_part: list of int
          :param non_repeating_part: the fractional part
          :type non_repeating_part: list of int
          :param int base: the base
  
          :returns: a Radix object with ``non_repeating_part`` rounded up
          :rtype: Radix
  
          Complexity: O(len(non_repeating_part + integer_part)
          """
          (carry, non_repeating_part) = \
             Nats.carry_in(non_repeating_part, 1, base)
          (carry, integer_part) = \
             Nats.carry_in(integer_part, carry, base)
          return Radix(
             sign,
             integer_part if carry == 0 else [carry] + integer_part,
             non_repeating_part,
             [],
             base,
             False
          )