One final thing to note about the inference algorithm is that the notion of permissibility for a transition t out of a configuration c can be used to capture not only formal constraints on transitions -such as the fact that it is impossible to perform a SHIFT p transition with an empty buffer or illegal to perform a LEFT-ARC d transition with the special root node on top of the stack -but also to filter out unlike-ly dependency labels or tags.
in the experiments later on, we will typically constrain the parser so that SHIFT p is permissible only if p is one of the k best part-of-speech tags with a score no more than α below the score of the 1-best tag, as determined by a preprocessing tagger.