Extending Graphplan to Domain Axiom Planning

This short paper proposes an extension of the Graphplan [1] planning system. The extension allows Graphplan to solve planning problems containing Domain Axioms (DAs) in the form p1 ∧ p2 ∧...∧ pn→ c. The problem of DAs arises when the domain representation language adopted is augmented with more expressive terms. For example, in the blocks-world domain, if the set of blocks present in the initial state is unknown, it is not possible to fully express the condition/goal “block A is on the same pile of block B” using only the terms on(x,y), clear(x) and on-table(x). On the other hand, if the terms above(x,y) or under(x, y) (with their obvious meaning) are introduced in the domain definition language, the planning problem needs to be augmented with the following domain axioms: