Definition 4.4 (Label-tuple) Let G be a pq-gram with the nodes V (G) = {v1, ...
Definition 4.4 (Label-tuple) Let G be a pq-gram with the nodes V (G) = {v1, ... , vp, vp+1, ... , vp+q}, where vi is the i-th node in preorder. The tuple l(G) = (l(v1), ... , l(vp), l(vp+1), ... , l(vp+q)) is called the label-tuple of G.