In order to determine which actions are appropriate to satisfy a subgoal g in the goal stack associated with mental situation m, STRIPS tries to prove the subgoal from the formulas in the database associated with the current situation using resolution. If the subgoal cannot be proved, it selects those actions whose add lists contain the largest number of predicates that can be resolved against the clauses in the incompleted proof of the subgoal. Instead of doing this, we provide an explicit definition of the predicate Appr (for appropriate) that selects the same actions for the blocks world example considered.
