AtD uses a lot of memory but this technique made a difference speeding up the spell checker. For things best done with a hash lookup, we use hashtables. This is what we're using for generating edits still (I wrote most of this post in August 09, finally finished it today).<p>[Edit: I wrote Sleep :) I don't promote it much but it's been with me for many years and I've applied it to a lot of problems including the NLP in AtD]