Prodigy planning algorithm

We present a formal description of the planning algorithm used in the Prodigy4.0 system. The algorithm is based on an interesting combination of backward-chaining planning and simulation of plan execution. The backward-chainer selects goal-relevant operators, and then Prodigy simulates their application to the current state of the world. The system can use di erent backward-chaining procedures, some of which are presented in the paper. This research is sponsored by the Wright Laboratory, Aeronautical Systems Center, Air Force Materiel Command, USAF, and the Advanced Research Projects Agency (ARPA) under grant number F33615-931-1330. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the o cial policies or endorsements, either expressed or implied, of Wright Laboratory or the U. S. Government. The U. S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon. This manuscript is submitted for publication with the understanding that the U. S. Government is authorized to reproduce and distribute reprints for Governmental purposes.