10.1 Variables for edge labels

There are already implicit ('don't care') variables for edge labels, i.e. the unlabelled dominance operator > and the dominance wildcard >* etc. If explicit variables for edge labels were available, the user could require co-reference of edge labels. To us it is unclear what kind of computational complexity will be introduced by this additional expressivity. And furthermore, there is a work-around: Since the number of edge labels (grammatical functions) tends to be rather small, it does not seem too inconvenient to define appropriate templates which enumerate pairs of edges with the same labels.