  We introduce Ak, an extension of the action description language A (Gelfond
and Lifschitz, 1993) to handle actions which affect knowledge. We use sensing
actions to increase an agent's knowledge of the world and non-deterministic
actions to remove knowledge. We include complex plans involving conditionals
and loops in our query language for hypothetical reasoning. We also present a
translation of Ak domain descriptions into epistemic logic programs.
