We define an left-open edge, <w,v] of a GST as the edge that contains nodes between the upper node Lemma lc: Each substring that terminates in a node between a left-open edge <w, v] has the same tf and df.
a left-open edge <w, v] of the GST has a upper node w and lower node v. The substring "aca" that terminates in <w, v] has a counts of 3;2, whose occurrences are underlined in each of the strings in the GST.