code: def fix_e713(self, result):
          
          (line_index, offset, target) = get_index_offset_contents(result,
                                                                   self.source)
  
          # to convert once 'not in' -> 'in'
          before_target = target[:offset]
          target = target[offset:]
          match_notin = COMPARE_NEGATIVE_REGEX_THROUGH.search(target)
          notin_pos_start, notin_pos_end = 0, 0
          if match_notin:
              notin_pos_start = match_notin.start(1)
              notin_pos_end = match_notin.end()
              target = '{}{} {}'.format(
                  target[:notin_pos_start], 'in', target[notin_pos_end:])
  
          # fix 'not in'
          match = COMPARE_NEGATIVE_REGEX.search(target)
          if match:
              if match.group(3) == 'in':
                  pos_start = match.start(1)
                  new_target = '{5}{0}{1} {2} {3} {4}'.format(
                      target[:pos_start], match.group(2), match.group(1),
                      match.group(3), target[match.end():], before_target)
                  if match_notin:
                      # revert 'in' -> 'not in'
                      pos_start = notin_pos_start + offset
                      pos_end = notin_pos_end + offset - 4     # len('not ')
                      new_target = '{}{} {}'.format(
                          new_target[:pos_start], 'not in', new_target[pos_end:])
                  self.source[line_index] = new_target
docs: Fix (trivial case of) non-membership check.