When pattern X is allowed, both m a and m b are not directly associated with any natural language word, so we are able to further insert arbitrarily many (compatible) semantic units between the two units m a and m b while the resulting relaxed hybrid tree remains valid.
results showed that our system consistently yielded higher results than all the previous systems, including our state-of-the-art relaxed hybrid tree system (the full model, when all the features are used), in terms of both accuracy score and F 1measure.