(ontable a), (holding a), (on a b), (on a c), (on a d)
(ontable b), (holding b), (on b a), (on b c), (on b d)
(ontable c), (holding c), (on c a), (on c b), (on c d)
(ontable d), (holding d), (on d a), (on d b), (on d c)