Let us consider the meaning of {j, i, "O"} if the head of the j-th bunsetsu is the k-th one such that j < k < i.
in the context of the algorithm in Figure 3, {j, i, "O"} actually means that the j-th bunsetsu modifies th l-th one such that i < l. "O" does not simply mean that two bunsetsus does not have a dependency relation.