Pre-processing planning domains containing Language Axioms

We present an automatic procedure for pre-processing planning problems containing language axioms, a specific type of domain axioms. The axioms considered are assumed to be in the form p1 ∧ p2 ∧ ...∧ pn → c. The pre-processing approach described consists of encoding the language axioms directly inside the given operators, contrary to other (not always correct) existing approaches in which axioms are converted into additional operators. A distinction is made between two different types of axiom sets, namely, recursive and non-recursive sets, which are treated differently. While a simple replacement algorithm is appropriate for the nonrecursive case, a more sophisticated procedure is proposed for pre-processing sets of recursive language axioms. Subject to some assumptions, the method presented can be generalised and used with any set of axioms of the type considered. Preliminary experimental results seem to suggest that the approach identified is sound and may lead to improvements in planning performance.