(define (domain blocksworld)
  (:requirements :strips) 		; STRIPS required
  (:predicates (on ?x ?y) 		; block ?x is on block ?y
	       (ontable ?x)		; block ?x on the table
	       (clear ?x)		; no block is on block ?x
	       (handempty)		; robot’s arm is empty
	       (holding ?x)		; robot’s arm is holding ?x
	       )
  (:action pick-up			; action „pick up from the table”
	     :parameters (?block)
	     :precondition (and (clear ?block) (ontable ?block) (handempty))
	     :effect
	     (and (not (ontable ?block))
		  (not (clear ?block))
		  (not (handempty))
		  (holding ?block)))
  (:action put-on-table			; action „put on the table”
	     :parameters (?block)
	     :precondition  (holding ?block)
	     :effect
	     (and (ontable ?block)
		  (clear ?block)
		  (handempty)
		  (not(holding ?block)))
  (:action put-on-block			; action „put block A on block B”
	     :parameters (?blockA, ?blockB)
	     :precondition  (holding ?blockA)
	     :effect
	     (and (on ?blockA ?blockB)
		  (not (clear ?blockB))
		  (handempty)
		  (not(holding ?blockA)))
  (:action pick-up-from-block			; action „take block A off block B”
	     :parameters (?blockA ?blockB)
	     :precondition (and (clear ?blockA) (on ?blockA ?blockB) (handempty))
	     :effect
	     (and (not (on ?blockA ?blockB))
		  (not (clear ?blockA))
		  (not (handempty))
		  (holding ?blockA))
		  (clear ?blockB))
)

(define (problem easy)
  (:domain blocksworld)
  (:objects a b c)
  (:init (ontable a) (ontable b) (ontable c) (clear a) (clear b) (clear c) (handempty))
  (:goal (and (on b c) (on a b)))
)

(define (problem medium)
  (:domain blocksworld)
  (:objects a b c)
  (:init (on a c) (ontable b) (ontable c) (clear a) (clear b) (handempty))
  (:goal (and (on b c) (on a b)))
)

(define (problem hard)
  (:domain blocksworld)
  (:objects a b c)
  (:init (on c a) (ontable a) (ontable b) (clear b) (clear b) (handempty))
  (:goal (and (on b c) (on a b)))
)