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 <cite>relaxed hybrid tree</cite> remains valid. Therefore we can construct a <cite>relaxed hybrid tree</cite> representation that contains the given natural language sentence w 1 w 2 with an infinite number of nodes.