Easy and Hard Conformant Planning

Even under polynomial restrictions on plan length, conformant planning remains a very hard computational problem as plan verification itself can take exponential time. This heavy price cannot be avoided in general although in many cases conformant plans are verifiable efficiently by means of simple forms of disjunctive inference. We report an efficient but incomplete planner capable of solving non-trivial problems quickly. In this work, we show that this is possible by mapping conformant into classical problems that are then solved by an off-the-shelf classical planner. The formulation is sound as the classical plans obtained are all conformant, but it is incomplete as the inverse relation does not always hold. Atoms L/Xi that represent conditional beliefs ’if Xi then L’ are introduced in the classical encoding and combined with suitable actions when certain invariants are verified. Empirical results over a wide variety of problems illustrate the power of the approach. We propose extensions to this formulation.