[ PrepositionChain wd index;
  if (line_tdata-->index == wd) return wd;
  if ((line_token-->index)->0 & $20 == 0) return -1;
  do
  {   if (line_tdata-->index == wd) return wd;
      index++;
  }
  until ((line_token-->index == ENDIT_TOKEN)
         || (((line_token-->index)->0 & $10) == 0));
  return -1;
];