An Representation Trick
Since we’re talking about doing things rather than states, we transform the initial state and goal state description into “pseudo-actions”
The action initial has no preconditions, and its postconditions are exactly what is true initially
The action goal has the goal as a precondition, and no postconditions
There is exactly one instance of initial in every plan, and it must be “executed” first
There is exactly one instance of goal in every plan, and it must be “executed” last