Consider a database of rules used for route planning for air strikes. Suppose it needs to be modified with the fact that F-117 engines are particularly vulnerable to flying through air loaded with volcanic ash. We suppose that the need for operations near active volcanos had not been anticipated. Adding rules that F-117s should not go within 5 miles of a visible plume or 50 miles downwind from the volcano might be one solution. However, if the enemy was trying to avoid air attack by operating near the volcano might require refining the rule or being able to use the facts to take into account new rules weighing the urgency of the mission against the risk of damage to the airplanes.
Ideally the rules could be added without detailed knowledge of existing rules, but this is unlikely. A system that could plan using the bare facts about damage to F-117 engines would be more readily modified to take volcanic ash into account.
The Formal Reasoning Group sees elaboration tolerance, used in the above manner, as a key tool for testing HPKB's, especially as they are used in planning..