while pushing the productions represented by the tree arcs on a stack as they are
encountered. Applying this technique to the search tree in Figure 11.7 produces
the stack of productions in Figure 11.8. The control system can now solve the
puzzle in the outside world by executing the instructions as they are popped
from this stack.
There is one more observation that we should make. Recall that the trees we
discussed in Chapter 8 use a pointer system that points down the tree, thereby
allowing us to move from a parent node to its children. In the case of a search