  We present an epistemic action theory for tractable epistemic reasoning as an
extension to the h-approximation (HPX) theory. In contrast to existing
tractable approaches, the theory supports functional fluents and postdictive
reasoning with static causal laws. We argue that this combination is
particularly synergistic because it allows one not only to perform direct
postdiction about the conditions of actions, but also indirect postdiction
about the conditions of static causal laws. We show that despite the richer
expressiveness, the temporal projection problem remains tractable (polynomial),
and therefore the planning problem remains in NP. We present the operational
semantics of our theory as well as its formulation as Answer Set Programming.
