# Event Calculus Planning Revisited

# Murray Shanahan

## Abstract

In 1969 Cordell Green presented his seminal description of planning as
theorem proving with the situation calculus. The most pleasing feature of
Green's account was the negligible gap between high-level logical
specification and practical implementation. This paper attempts to
reinstate the ideal of planning via theorem proving in a modern guise. In
particular, I will show that if we adopt the event calculus as our logical
formalism and employ abductive logic programming as our theorem proving
technique, then the computation performed mirrors closely that of a
hand-coded partial order planning algorithm. Furthermore, if we extend the
event calculus in a natural way to accommodate compound actions, then
using exactly the same abductive theorem prover we obtain a hierarchical
planner. All this is a striking vindication of Kowalski's slogan
"Algorithm = Logic + Control".