code: def pre_filter(self):
          
          inner = self._inner.pre_filter()
          if inner:
              if inner.startswith('"not=$') and inner.endswith('"') and '\\' not in inner:
                  return inner[6:-1]  # double negation, return inner command
              elif inner.startswith('"'):
                  inner = '"$' + inner[1:]
              else:
                  inner = '$' + inner
              return 'not=' + inner
          else:
              return ''
docs: Return rTorrent condition to speed up data transfer.