Operator Pruning Using Lifted Mutex Groups via Compilation on Lifted Level.

A lifted mutex group is a schematic first-order description of sets of facts such that each set contains facts out of which at most one can hold in any reachable state. It was previously shown that lifted mutex groups can be used for pruning of operators during grounding of PDDL tasks, i.e., it is possible to prune unreachable and dead-end operators even before the grounded representation is known. Here, we show that applying such a pruning technique does not require a modification of the grounding procedure. Instead, it is possible to compile the conditions under which we can use lifted mutex groups to prune operators directly into the preconditions of lifted actions on the PDDL level. In fact, we show that such compilation captures the pruning power of lifted mutex groups perfectly.