For instance, if we parse the sentence into spans [0, 4] and [4, 5], we have I(0, 4) = {1, 3, 4} and I(4, 5) = {5}, which adds up to a bag of 4 vertices at the node with span [0,5].
we also observe that while the span [0, 4] has three connections, to outside vertices, all of the connections are made to the same vertex 5.