  Planning as theorem proving in situation calculus was abandoned 50 years ago
as an impossible project. But we have developed a Theorem Proving Lifted
Heuristic (TPLH) planner that searches for a plan in a tree of situations using
the A* search algorithm. It is controlled by a delete relaxation-based domain
independent heuristic. We compare TPLH with Fast Downward (FD) and Best First
Width Search (BFWS) planners over several standard benchmarks. Since our
implementation of the heuristic function is not optimized, TPLH is slower than
FD and BFWS. But it computes shorter plans, and it explores fewer states. We
discuss previous research on planning within KR\&R and identify related
directions. Thus, we show that deductive lifted heuristic planning in situation
calculus is actually doable.
