Actors(A, B)
Init(At (A, LeftBaseline) ∧ At(B, RightNet ) ∧
Approaching (Ball, RightBaseline)) ∧ Partner (A, B) ∧ Partner (B, A)
Goal (Returned (Ball) ∧ (At(a, RightNet ) ∨ At (a, LeftNet ))
Action(Hit(actor , Ball),
PRECOND: Approaching (Ball, loc) ∧ At(actor , loc)
EFFECT: Returned (Ball))
Action(Go(actor , to),
PRECOND: At (actor , loc) ∧ to ≠ loc,
EFFECT: At (actor , to) ∧ ¬ At (actor , loc))
Figure ?? The doubles tennis problem. Two actors A and B are playing together and can be in one of four locations: LeftBaseline, RightBaseline, LeftNet , and RightNet . The ball can be returned only if a player is in the right place. Note that each action must include the actor as an argument.