A person on a downhill skateboard.
a person on a skateboard
person on a skateboard is the same as a person on a skateboard.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_skateboard(x2) & of(x2,x3) & n_downhill(x3) & n_person(x1))
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_skateboard(x2) & n_person(x1))