In order to find the sequence of edit operations that transforms one tree into another, such as the pair shown in Figure 1, the computation proceeds as follows: create a new matrix called δ 2 , which has the same dimensions as the matrix δ which is used to store the forest costs during ZS-TED to store the sequence of edit operations as a list.
when the values of δ are computed, the values of δ 2 are computed, by using the edit operation labels: "i" for an insertion, "d" for deletion, "x" for exchange and "m" for no operation (matching).