In other words, LEN is a stronger constraint than DEP in that the structures penalized by DEP are only a subset of structures penalized by LEN.
this bracket tree is not binarized; for example, we extract (X a b (X c d)) from the tree a b c d. table 2 shows the results, and we can see that DEP always performs the best, showing that DEP leads to the models that find better constituent structures.