To save some space, in the following we write right spinal trees horizontally and from left to right, as already done in Figure 3.
the grammar G 2 can alternatively be written as follows: For a node u in a right spinal tree derived by G 2 , we define We exploit this function to compute the excess of left parentheses over right parentheses in a sequence of nodes, and write: Let t be some right spinal tree in T(G 2 ), and let v be some node in t. Assume that u 1 , .