Comments on Search Algorithm

• The program continually goes deeper until it reaches a terminal state, which is either a goal or a failure.

• When the goal is found, search returns '() as its answer. This is an empty list of operators, since no operators are required to reach the goal.

• At each level as the search unwinds, the operator used at that level is put onto the front of the operator list using cons. cons adds a new item onto the front of a list:
  (cons 'a '(b c)) = (A B C)