(3) If l is the parent of k (Figure 6c), legal SHIFTs require all the words on the stack from l to the top to be reducable to k. (4) If l is a grand parent of k, all the words on the stack from l to the top will become descendants of l in the output (Figure 6e).
these words must be descendants of l in C, or the root of different subdependency trees.