code: def _match_replace_binary_combine(cls, a: list, b: list) -> list:
      
      if len(a) == 0 or len(b) == 0:
          return a + b
      r = _get_binary_replacement(a[-1], b[0], cls)
      if r is None:
          return a + b
      if r == cls._neutral_element:
          return _match_replace_binary_combine(cls, a[:-1], b[1:])
      if isinstance(r, cls):
          r = list(r.args)
      else:
          r = [r, ]
      return _match_replace_binary_combine(
          cls,
          _match_replace_binary_combine(cls, a[:-1], r),
          b[1:])
docs: combine two fully reduced lists a, b