A boy on a scooter.
The boy is on his scooter.
If a boy is  on a scooter does not imply that it is his.
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_scooter(x2) & n_boy(x1))
exists p1 x1 x2.(n_scooter(x2) & of(x2,x1) & n_male(x1) & n_boy(x1) & on(x1,x2))