When dealing with text, you can get a certain way with simple tricks. But eventually, a lack of any real model comes back and bites you. I recently saw a referal on this blog from a search on Google for
Google's results due to the 'AI' used in understanding the query, contained pages which didn't contain 'powerset' at all, but which contained some stem (for lack of a better word) such as 'powers'. You can get the results you intended if you put powerset in quotes as well (contrary to some belief that this is a crazy thing to do).