optimized for kind of achieving something looking more like generalization of a simple form of kind of combining these mixture models and so this is a good review paper if you ever want to kind of go back through the history of this and all the different methods develop there you start to get things that look more like representation learning and even multi-layer models so they'll start doing things like clustering over parts of speech or substituting for that so it's a very hand engineered way of potentially adding expressiveness but