From TWEAK to PWEAK: reducing the non linear planning framework

The TWEAK system (Chapman 87) is a very nice synthesis of a long trend in planning and Artificial Intelligence, including STRIPS (Fikes & Nilsson 71). We derive a correctness criterion which is simpler that the one used for TWEAK since it does not involve modal operators and does not introduce neither white knights nor separation. This criterion is compared to the one of TWEAK and other related works. We then derive a correct and complete planning procedure from this criterion, as it was done for TWEAK. The resulting planner is proved correct (it finds good plans), complete (it can find all possible plans with appropriate control) and shall always stop with a solution if there exists one. Moreover, this planner avoids some looping problems of TWEAK. This planner is implemented in Prolog and Lisp.