Reading CMU 07-380 Lecture 3: Classical Planning, PDDL, State-Space Search, and Relaxation Heuristics
07-380 Lec3 replaces propositional successor-state axioms with STRIPS actions (pre/add/del sets), which turns planning back into state-space search. When that search is too large, GraphPlan lets actions run in parallel and never deletes facts, and delete relaxation drops delete effects entirely, yielding the heuristics behind FF and Fast Downward.