A boy on a scooter.
The person is a boy.
Saying a boy is the same as saying the person.
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_scooter(x2) & n_boy(x1))
exists p1 x1.(n_person(x1) & exists x2.((x1 = x2) & n_boy(x2)))