A consumable resource is a resource that is (partially) used up by an action. For example, attaching engines to cars requires screws. The screws, once used, are not available for other attachments.
a. Explain how to modify the representation in Figure so that there are 100 screws initially, engine E1 requires 40 screws, and engine E2 requires 50 screws. The + and — function symbols may be used in effect literals for resources.
b. Explain how the definition of conflict between causal links and actions in partial-order planning must be modified to handle consumable resources.
c. Some actions—for example resupplying the factory with screws or refueling a car— can increase the availability of resources. A resource is monotonically non-increasing if no action increases it. Explain how to use this property to prune the search space.
