The preorder traversal of the tree in Figure 1 is the sequence {s 1 , s 2 , s 4 , s 3 , s 5 } and the sentential sequential order is {s 1 , s 2 , s 3 , s 4 , s 5 }.
according to the definition of Property 2: The preorder traversal of a document's discourse dependency tree takes into consideration the organization of a document respect to the dependencies between sentences.