  The classical representation of an AI planning problem, as described in  Amarel 1968,  evidently originates in early work of Herbert Simon’s, published in a 1966 CMU technical report,  Simon 1966.  In such a problem, an agent in an initial world-state is equipped with a set of actions, which are thought of as partial functions transforming world-states into world-states. Actions are feasible only in world-states that meet certain constraints.  (These constraints are now called the “preconditions” of the action.)  A planning problem then becomes a search for a series of feasible actions that successively transform the initial world-state into a desired world-state.